built-in

/B IH1 L T IH0 N/
noun
  1. 1

    Anything (such as a piece of furniture, or a software feature) that is built in, not added as an extra.

adjective
  1. 1

    Constructed as a non-detachable 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.

Source: https://en.wiktionary.org/wiki/built-in