A register may refer to any of the following:
1. When referring to a CPU, the terms internal register, internal data bus, or register refer to how much information a processor can process at once. Instructions are allowed to flow at a rate that is as large as the register size, which is either 16, 32, or 64-bits wide.
As you can probably intuit, registers can only handle data that are smaller than their bit size. For example, if a program is designed to process 64-bit instructions, a processor with a 32-bit register would not be able to run that program.
2. Register is also a term that describes the process of sending information to a company about yourself or product you have purchased. Registering, in many cases, allows you access to technical support by a company or receive a free product or service.
Tip: Most companies do not require online registration, but product activation for operating systems is always required.
3. When referring to sound, a register refers to how high a note sounds. Essentially, a higher register means a higher pitch.