Tu B'Av (Hebrew: ט"ו באב, the fifteenth of the month Av) is a minor Jewish holiday. In modern-day Israel, it is celebrated as a holiday of love (Hebrew: חג האהבה, Hag HaAhava), similar to Valentine's Day. It is considered a very desirable date for Jewish weddings.
According to the Talmud, Tu B'Av was a joyous holiday in the days of the Temple in Jerusalem, marking the beginning of the grape harvest. Yom Kippur marked the end of the grape harvest. On both dates, the unmarried girls of Jerusalem would dress in white garments and go out to dance in the vineyards. (Babylonian Talmud, tractate Ta'anit 30b-31a)  That same section in the Talmud states that there were no holy days as happy for the Jews as Tu B'Av and Yom Kippur. The holiday celebrated the wood-offering brought in the temple (see Nehemiah 10:35). Josephus refers to it as the Feast of Xylophory ("Wood-bearing").
(... from Wikipedia on 2012-04-18 00:21:48)