If the fire alarm goes off in your building, be sure to join the exodus of people who are heading outside to the parking lot. This is a departure of a large number of people.
Exodus is the title of the second book of the Bible’s Old Testament in which the Israelites escape slavery in Egypt, but the term can refer to any sudden departure of a group of people. This noun is often coupled with the adjective mass, as in “mass exodus,” which usually indicates that almost everyone leaves at the same time. The reasons for this departure can be hostile, as during a war, or not, as when everyone exits the movie theater after the show's over.