Tisha b’Av is the anniversary of several tragic events in Jewish history. These include the destruction of the First Jerusalem Temple by the Babylonians in 586 BCE, the Second Jerusalem Temple by the Romans in 70 CE, the expulsion of the Jews from England in 1290 and from Spain in 1492.
The Hebrew words actually refer to the date, the 9th of Av. This falls in the summer, in July or August.
It is a fast day, second only in solemnity to Yom Kippur. In traditional synagogues the Book of Lamentations is read, and in earlier times, Jews would even put on sackcloth and cover their heads in ashes as a sign of mourning for the destruction of the Temple.
Liberal Jews tend not to take much notice of Tisha B’Av as Liberal Judaism rejects the traditional belief that the Temple should be rebuilt and re-established as the focus of Jewish worship. The fact that this date falls in the summer means that its observance is often limited to young people on summer camp.