Tisha B'Av (help·info) (Hebrew: תשעה באב‎ or ט׳ באב, "the Ninth of Av,") is an annual fast day in Judaism, named for the ninth day (Tisha) of the month of Av in the Hebrew calendar. The fast commemorates the destruction of both the First Temple and Second Temple in Jerusalem, which occurred about 655 years apart, but on the same Hebrew calendar date.^[1] Although primarily meant to commemorate the destruction of the Temples, it is also considered appropriate to commemorate other Jewish tragedies that occurred on this day, most notably the expulsion of the Jews from Spain in 1492.^[2] Accordingly, the day has been called the "saddest day in Jewish history".^[3]

Tisha B'Av falls in July or August in the western calendar. When the ninth of Av falls on Sabbath (Saturday), the observance is deferred to Sunday the tenth of Av. While the day recalls general tragedies which have befallen the Jewish people over the ages, the day focuses on commemoration of five events: the destruction of the two ancient Temples in Jerusalem, the sin of ten of the twelve scouts sent by Moses who spoke disparagingly about the Promised Land, the razing of Jerusalem following the siege of Jerusalem in 70 CE, and the failure of the Bar Kokhba revolt against the Roman Empire.

Revolution Day or the Day of the Revolution refers to public holidays or remembrance days in various country held in commemoration of an important event in the country's history, usually the starting point or a turning point in a revolution that led to significant political change.

The leap day in the French Republican Calendar, in use for several years after the French Revolution, added after a franciade, is also known as "Revolution Day" (Jour de la Révolution or Fête de la Révolution in French). See Sansculottides for details.

Pi Day is an unofficial holiday commemorating the mathematical constant π (pi). Pi Day is celebrated on March 14 (or 3/14 in month/day date format), since 3, 1 and 4 are the three most significant digits of π in the decimal form. In 2009, the United States House of Representatives supported the designation of Pi Day.^[2]

Pi Approximation Day is held on July 22 (or 22/7 in day/month date format), since the fraction ²²⁄₇ is a common approximation of π.^[3]

In the province of Quebec, Canada, the Construction Holiday is the most popular time for summer vacations.

In 1970, Quebec legislated an annual holiday for the construction industry which begins the 2nd last Sunday of July every year lasting for a period of 2 weeks, and the holiday came into effect officially in the summer of 1971. Many Quebecers outside the construction industry also take their holidays during these two weeks, and it is the busiest time of year for the province's tourism industry, with a surge of up to 40% in activity at some sites.