Lambda or lamda (uppercase , lowercase ? ; ? Greek: (?) lám(b)da) is the 11th letter of the Greek alphabet, representing the sound /l/. In the system of Greek numerals lambda has a value of 30. Lambda is derived from the Phoenician Lamed . Lambda gave rise to the Latin L and the Cyrillic El (?). The ancient grammarians and dramatists give evidence to the pronunciation as ( [la:bda:] ) in Classical Greek times. In  Modern Greek the name of the letter, , is pronounced .
early Greek alphabets, the shape and orientation of lambda varied. Most variants consisted of two straight strokes, one longer than the other, connected at their ends. The angle might be in the upper-left, lower-left ("Western" alphabets), or top ("Eastern" alphabets). Other variants had a vertical line with a horizontal or sloped stroke running to the right. With the general adoption of the  Ionic alphabet, Greek settled on an angle at the top; the Romans put the angle at the lower-left.
The HTML 4 character entity references for the Greek capital and small letter lambda are
The Unicode code points for lambda are U+039B and U+03BB.
The Greek alphabet on a
black figure vessel
, with a Phoenician-lamed-shaped lambda. The gamma has the shape of modern lambda.
Upper-case letter ?
Examples of the symbolic use of uppercase lambda include:
lambda particle is a type of subatomic particle in subatomic particle physics. Lambda is the set of logical axioms in the
axiomatic method of logical deduction in first-order logic. Lambda was used as a
shield pattern by the Spartan army. This stood for Lacedaemon ( , ? Lakedaím?n), the name of the polis of the Spartans, as opposed to the city itself. Lambda is the
von Mangoldt function in mathematical number theory. In
statistics, Wilks's lambda is used in multivariate analysis of variance ( MANOVA analysis) to compare group means on a combination of dependent variables. In the
spectral decomposition of matrices, lambda indicates the diagonal matrix of the eigenvalues of the matrix. In
computer science, lambda is the time window over which a process is observed for determining the working memory set for a digital computer's virtual memory management. In
astrophysics, lambda represents the likelihood that a small body will encounter a planet or a dwarf planet leading to a deflection of a significant magnitude. An object with a large value of lambda is expected to have cleared its neighborhood, satisfying the current definition of a planet. In
crystal optics, lambda is used to represent the period of a lattice. In
NATO military operations, a chevron (a heraldic symbol which looks like a capital letter lambda or inverted V) is painted on the vehicles of this military alliance for identification. In
chemistry there are ? (delta) and ? (lambda) isomers, see: coordination complex In
electrochemistry, lambda denotes the "equivalent conductance" of an electrolyte solution. In
cosmology, lambda is the symbol for the cosmological constant, a term added to some dynamical equations to account for the acceleration of the universe. In optics, lambda denotes the grating pitch of a
Bragg reflector. In block-handwritten
Russian, this letter represents ? in both uppercase and lowercase. In politics the lambda is the symbol of Identitarianism, a white nationalist movement that originated in France before spreading out to the rest of Europe and later on to North America, Australia and New Zealand. The Identitarian lambda represents the Battle of Thermopylae.
Lower-case letter ?
Examples of the symbolic use of lowercase lambda include:
Lambda indicates the
wavelength of any wave, especially in physics, electronics engineering, and mathematics.  In
evolutionary algorithms, ? indicates the number of offspring that would be generated from ? current population in each generation. The terms ? and ? are originated from Evolution strategy notation. Lambda indicates the
radioactivity decay constant in nuclear physics and radioactivity. This constant is very simply related (by a multiplicative constant) to the half-life of any radioactive material. In probability theory, lambda represents the density of occurrences within a time interval, as modeled by the
Poisson distribution. In
mathematical logic and computer science, lambda is used to introduce anonymous functions expressed with the concepts of lambda calculus.
Lambda is a unit of volume, synonymous with one micro liter (1 ?L), that is, one cubic millimetre (1 mm 3). This use is currently deprecated. Lambda indicates an
eigenvalue in the mathematics of linear algebra. In the physics of
electric fields, lambda sometimes indicates the linear charge density of a uniform line of electric charge (measured in coulombs per meter). Lambda denotes a
Lagrange multiplier in multi-dimensional calculus. In
solid-state electronics, lambda indicates the channel length modulation parameter of a MOSFET. In
ecology, lambda denotes the long-term intrinsic growth rate of a population. This value is often calculated as the dominant eigenvalue of the age/size class matrix (mathematics). In
formal language theory and in computer science, lambda denotes the empty string. Lambda is a nonstandard symbol in the
International Phonetic Alphabet for the voiced alveolar lateral affricate . Lambda denotes the
Lebesgue measure in mathematical set theory. The
Goodman and Kruskal's lambda in statistics indicates the proportional reduction in error when one variable's values are used to predict the values of another variable. Lambda denotes the
oxygen sensor in a vehicle that measures the air-to-fuel ratio in the exhaust gases of an internal-combustion engine. A
Lambda 4S solid-fuel rocket was used to launch Japan's first orbital satellite in 1970.  Lambda denotes the
failure rate of devices and systems in reliability theory, and it is measured in failure events per hour. Numerically, this lambda is also the reciprocal of the mean time between failures. In criminology, lambda denotes an individual's frequency of
offenses. In cartography and navigation, lambda denotes the
longitude of a location. In
electrochemistry, lambda also denotes the ionic conductance of a given ion (the composition of the ion is generally shown as a subscript to the lambda character). In
neurobiology, lambda denotes the length constant (or exponential rate of decay) of the electric potential across the cell membrane along a length of a nerve cell's axon. In the science and technology of
heat transfer, lambda denotes the heat of vaporization per mole of material (a.k.a. its "latent heat").  In the technology and science of celestial navigation, lambda denotes the longitude as opposed to the Roman letter "L", which denotes the
latitude. A block style lambda is used as a recurring symbol in the
Valve computer game series , Half-Life referring to the Lambda complex of the fictional  Black Mesa Research Facility, as well as making appearances in the sequel Half-Life 2.  In 1970, a lowercase lambda was chosen by Tom Doerr as the symbol of the New York chapter of the Gay Activists Alliance.  The lambda symbol became associated with  Gay Liberation  and recognized as an  LGBT symbol for some time afterwards, being used as such by the International Gay Rights Congress in Edinburgh, the gay rights organization  Lambda Legal, and the Lambda Literary Foundation, among others.
Roman libra and Byzantine lítra ( ), which served as both the pound mass unit and liter volume unit, were abbreviated in Greek using lambda with modified forms of the iota subscript (as ). These are variously encoded in Unicode. The Ancient Greek Numbers Unicode block includes 10183 (?) as well as ?, which is described as 10162 GREEK LITRA SIGN GREEK ACROPHONIC HERMIONIAN TEN but was much more common as a form of the litra sign. A variant of the sign can be formed from 0338  and either 039B COMBINING LONG SOLIDUS OVERLAY () or 03BB GREEK CAPITAL LETTER LAMDA (). GREEK SMALL LETTER LAMDA 
Unicode uses the spelling "lamda" in character names, instead of "lambda", due to "preferences expressed by the Greek National Body".
 Greek Lambda / Coptic Laula
GREEK CAPITAL LETTER LAMDA
GREEK SMALL LETTER LAMDA
GREEK LETTER SMALL CAPITAL LAMDA
COPTIC CAPITAL LETTER LAULA
COPTIC SMALL LETTER LAULA Encodings
UTF-8 206 155
225 180 167
E1 B4 A7
226 178 150
E2 B2 96
226 178 151
E2 B2 97
Numeric character reference Λ
Named character reference Λ
DOS Greek 138
DOS Greek-2 182
MATHEMATICAL BOLD CAPITAL LAMDA
MATHEMATICAL BOLD SMALL LAMDA
MATHEMATICAL ITALIC CAPITAL LAMDA
MATHEMATICAL ITALIC SMALL LAMDA
MATHEMATICAL BOLD ITALIC CAPITAL LAMDA
MATHEMATICAL BOLD ITALIC SMALL LAMDA Encodings
UTF-8 240 157 154 178
F0 9D 9A B2
240 157 155 140
F0 9D 9B 8C
240 157 155 172
F0 9D 9B AC
240 157 156 134
F0 9D 9C 86
240 157 156 166
F0 9D 9C A6
240 157 157 128
F0 9D 9D 80
UTF-16 55349 57010
Numeric character reference 𝚲
MATHEMATICAL SANS-SERIF BOLD CAPITAL LAMDA
MATHEMATICAL SANS-SERIF BOLD SMALL LAMDA
MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL LAMDA
MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL LAMDA Encodings
UTF-8 240 157 157 160
F0 9D 9D A0
240 157 157 186
F0 9D 9D BA
240 157 158 154
F0 9D 9E 9A
240 157 158 180
F0 9D 9E B4
UTF-16 55349 57184
Numeric character reference 𝝠
These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.
^ Herbert Weir Smyth.
A Greek Grammar for Colleges. I.1.c
"Epigraphic Sources for Early Greek Writing". Poinikastas.CSAD.ox.ac.uk . Retrieved .
"HTML 4.01 Specification. 24. Character entity references in HTML 4". World Wide Web Consortium.
Nelkon, Michael (1977). Fundamentals of Physics. St. Albans, Hertfordshire: Hart-Davis Educational. p. 329.
"Encyclopedia Astronautica: Lambda". Astronautix.com. Archived from the original on 2012-10-22 . Retrieved .
^ Wankat Separation Process Engineering 2nd ed, Prentice Hall
"Half-Life on Steam". store.steampowered.com. Valve . Retrieved .
"Half-Life 2 on Steam". store.steampowered.com. Valve . Retrieved .
Rapp, Linda (2004). "Gay Activists Alliance" (PDF). glbtq.com.
"1969, The Year of Gay Liberation". The New York Public Library. June 2009 . Retrieved 2018.
Goodwin, Joseph P. (1989). "It Takes One to Know One". . Indiana University Press. p. More Man Than You'll Ever Be: Gay Folklore and Acculturation in Middle America 26. ISBN . 978-0253338938
Rapp, Linda (2003). "Symbols" (PDF). glbtq.com.
Haggerty, George E., ed. (2000). (1 ed.). London: Garland Publishing. p. Gay Histories and Cultures: An Encyclopedia (Encyclopedia of Gay Histories and Cultures, Volume II) 529. ISBN . 0-8153-1880-4 OCLC 750790369.
Unicode Ancient Greek Numbers block.
"Thesaurus Linguae Graecae" (PDF). Stephanus.TLG.UCI.edu. Archived from the original (PDF) on 2011-07-16.