built-in

1. not comparableConstructed as a nondetachable part of a larger structure.
2. not comparableBeing an essential and permanent part of something.

   Synonyms: instilled

3. not comparableBeing an included feature that normally comes as an extra.

   Synonyms: incorporated, integrated

plural built-ins

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

   Still, some commenters were quick to criticize the trend, arguing that bookshelf wealth simply indicates you have the financial means (and the space for a built-in) and that it can lean inauthentic.

   2024 February 5, Angela Tafoya, “Is "Bookshelf Wealth" the Most Authentic TikTok Interiors Trend Yet?”, in Vogue, New York, N.Y.: Condé Nast Publications, →ISSN, →OCLC, archived from the original on 12 Feb 2024

2. computingA function that is built into a system.

   1 more example

   „If FUNCTION is a string starting with CORE::, the rest is taken as a name for a Perl builtin. If the builtin's arguments cannot be adequately expressed by a prototype (such as system), prototype() returns undef, because the builtin does not really behave like a Perl function. Otherwise, the string describing the equivalent prototype is returned.“

   2015 February 26 (last accessed), “prototype”, in (Please provide the book title or journal name) (HTML), perldoc.perl.org