Triple metre (or Am. triple meter, also known as triple time) is a musical metre characterized by a primary division of 3 beats to the bar, usually indicated by 3 (simple) or 9 (compound) in the upper figure of the time signature, with 3
2, and 3
8 being the most common examples. The upper figure being divisible by three does not of itself indicate triple metre; for example, a time signature of 6
8 usually indicates compound duple metre, and similarly 12
8 usually indicates compound quadruple metre.
It is reasonably common in ballads and classical music but much less so in traditions such as rock & roll and jazz. The most common time in rock, blues, country, funk, and pop is quadruple. Jazz writing has become more adventurous since Dave Brubeck's album Time Out,  One noteworthy example of a jazz classic that employs triple metre is John Coltrane's version of "My Favorite Things". 
Movements in triple time characterized the more adventurous approach of 17th- and 18th-century music, for example the sarabande, which originated in Latin America and appeared in Spain early in the 16th Century, became a standard movement in the suite during the Baroque period. The Baroque sarabande is commonly a slow triple rather than the much faster Spanish original, consistent with the courtly European interpretations of many Latin dances.
There are many classical works in triple metre. Joseph Haydn's "Farewell" Symphony is an interesting case, as the first three movements are all in triple meter, as is the "farewell" section of the final movement.
In hymns and other religious works it is still common, with tunes such as Dave Bilborough's Abba, Father following from more traditional melodies such as Slane (adapted form a traditional Irish melody), Cloisters (written in the 16th Century), Amazing Grace and Rock of Ages.
In contemporary pop traditions (Soul, Rap, R&B, Rock) triple metre is much less common but examples do exist:
Some album titles reference the time signature like Jimmy Buffett's third album Living and Dying in 3/4 Time, jazz drummer Max Roach's Jazz in 3/4 Time and Davey Graham and Alexis Korner's 1962 EP 3/4 AD .