built-in

Short definition from Wiktionary

Adjective

1. 1
   Constructed as a nondetachable part of a larger structure.
2. 2
   Being an essential and permanent part of something.
3. 3
   Being an included feature that normally comes as an extra.
4. 4
   Alternative spelling of built-in.

Noun

1. 1
   Anything (such as a piece of furniture, or a software feature) that is built in, not added as an extra.
2. 2
   A function that is built into a system.