Definition of register

1. a row of flip-flops used to store a group of binary digits while the computer is processing them. (See flip-flop.) A flip-flop can be in either of two states, so one flip-flop can store 1 bit.A register consisting of 16 flip-flops can store words that are 16 bits long.
2. to inform a manufacturer of a purchase (see registration, definition 1).

The word register has many other meanings in business and education; only those specific to computers are covered here.

record of debit or industrial insurance policies.

Business: record a trademark, patent, copyright, etc., with a government agency in order to claim exclusivity.
Printing: align color plates correctly in order to print a perfect color reproduction of artwork. The print is "in register" when it is faithful to the original. When it is "out of register," it may be blurry and look like a 3-D comic book picture.