Today is a the 9th day of the Jewish month of Av, and it is a fasting holiday known as Tisha B’Av. This is not a joyous holiday, but a day of mourning in which the Jews remember the destruction of the First and Second Temple as well as other tragedies in Jewish history including the Bar Kochba revolt (learn more about that here http://www.chabad.org/library/article_cdo/aid/144572/jewish/The-Fall-of-Betar.htm )and the expulsion of the Jews from England in 1290 and Spain in 1492.
There are certain rules and regulations that must be followed on this day. Some prohibited things include eating, wearing leather, bathing, or greeting one another. Work is not prohibited but discouraged, and only the sad portions of Torah are allowed to be studied.
Learn more about the holiday at these sites.