In a regular (kesidran) year Kislev has 30 days, but because of the Rosh Hashanah postponement rules, in some years it can lose a day to make the year a "short" (chaser) year. Kislev is an autumn month which occurs in November-December on the Gregorian calendar and is sometimes known as the month of dreams.
The name of the month derives from Akkadiankislimu. But some popular etymologies connect it to the Hebrew root K-S-L as in the words "kesel, kisla" (hope, positiveness) or "ksil" (Orion, a constellation that shines especially in this month) because of the expectation and hope for rains.
In Jewish Rabbinic literature, the month of Kislev is believed to correspond to the Tribe of Benjamin.
^"Now the fifteenth day of the month Kislev, in the hundred forty and fifth year, they set up the abomination of desolation upon the altar, and builded idol altars throughout the cities of Judah on every side." (1 Maccabees 1:54)