What is Voter Caging?

Legal Definition
Voter caging refers to challenging the registration status of voters and calling into question the legality of allowing them to vote. Sometimes, it involves sending direct mail to the addresses of registered voters and compiling a list of addressees from which the mail is returned undelivered. The list is then used to purge or challenge voters' registrations on the grounds that the voters do not legally reside at the registered addresses.

In the United States, the practice is legal in many states. However, it has been challenged in the courts for perceived racial bias, and it has been declared illegal under the Voting Rights Act of 1965.

The term has also been applied to recent cases of increased requirements for proof of identity, residency, and eligibility being added with the intent to limit the number of eligible voters.
-- Wikipedia