A mitzvah is a rule or commandment. The plural of “mitzvah” is “mitzvot”.
The Torah lists 613 mitzvot. Of these, 365 are things that Jews must not do (negative mitzvot). The other 248 are things that Jews must do (positive mitzvot). The most famous list of the 613 mitzvot was written by Maimonides.
Some of the mitzvot are about how people must act to other people. For example, they must give charity to a poor person, or help a person who is in danger.
Some mitzvot are about how people must act towards G-d. For example, they must respect G-d’s name, or not work on the Sabbath.
Some mitzvot are for everyday life, and some are ‘time bound’ (only for special times), such as holidays.
Across history and today, the requirements for different mitzvot have been debated. Different denominations interpret mitzvot in different ways. Different individuals observe mitzvot in different ways (or not at all).
In common use, mitzvah also refers to the deed done to perform to fulfil a commandment.
Text adapted from Simple English Wikipedia, Creative Commons Attribution-ShareAlike License 4.0.
Casale Monferrato - Synagogue -Sefer Torah. Photo by FLLL on Wikimedia Commons, CC-BY-SA 3.0.