What is the Jewish fast observed before Purim in memory of Esther’s fast called?

The Jewish fast observed before Purim in memory of Esther’s fast is called Ta'anit Esther.

Ta'anit Esther, or the Fast of Esther, is a minor Jewish fast usually observed on the day before Purim. Its name refers to Esther’s call for the Jews of Shushan to fast before she approached King Ahasuerus, as described in the Book of Esther. The fast is therefore linked to the story’s communal preparation and appeal for divine help.

Unlike Yom Kippur, Ta'anit Esther is generally a daylight fast rather than a fast beginning the previous evening. Its observance can be moved when the usual date conflicts with Shabbat, since public fasting is not held on Shabbat except for Yom Kippur.

Ta'anit Esther is not the same as the Fast of Gedalia, which follows Rosh Hashanah, or Tisha B'Av, which commemorates major historical tragedies including the destruction of the Temples. People who are ill, pregnant, nursing, or otherwise medically unable to fast may have different exemptions under Jewish law.