A more thorough explanation:

Definition: Reapportionment is the process of redrawing the boundaries of legislative districts to reflect changes in population.

For example, let's say that a state has 10 congressional districts, each with roughly the same number of people. Over time, some districts may become more populous than others due to factors such as migration or birth rates. Reapportionment would involve adjusting the boundaries of these districts so that each one has roughly the same number of people again.

Reapportionment is required by the U.S. Constitution, which mandates that congressional districts be reapportioned every 10 years based on the results of the census. This ensures that each state is represented fairly in Congress and that each person's vote carries roughly the same weight.

Reapportionment is sometimes confused with gerrymandering, which is the practice of drawing district boundaries in a way that favors one political party or group over another. While gerrymandering can occur during the reapportionment process, it is not the same thing as reapportionment itself.