Voter registration is the requirement in some democracies for citizens and residents to check in with some central registry specifically for the purpose of being allowed to vote in elections. An effort to get people to register is known as a voter registration drive.
In democracies where resident registration is in effect, voter registration is generally not required.
Read more about Voter Registration: Centralized/compulsory Vs. Opt-in, Same-day Voter Registration or Election Day Registration, Effects and Controversy, Registration of Voters in Various Countries