1. To enter one's name into an official record as having some particular status. I registered as a democrat when I first started voting, but I'm thinking of switching my registration to a libertarian. Because of the conviction, he will be forced to register as a sex offender for the next 10 years.

2. To enter someone's name into an official record as having some particular status. Often used in passive constructions. In this usage, a noun or pronoun is used between "register" and "as." We'll first have to register you as a patient before we can begin any treatments. She's registered as a director in the company.