Passover (in Hebrew: Pesach) is today perhaps the most important of the three agricultural festivals deliniated in the Torah (the other two being Shavuot and Sukkot). It is celebrated each year begininning on the 15th of Nissan, which may fall anytime from early to late spring. By astronomical measures, the 15th of Nissan is the first full moon after the spring solstice.
Observances associated with Pesach include the selling of chametz, eating of matzah (unleavened bread), and other ritual foods, and reading from the Haggadah.
Pesach commemorates the Exodus from Egypt.