ASDF - another system definition facility - is the de facto standard build system for common lisp.

https://asdf.common-lisp.dev/

In common lisp, you don't need a build system at all; you can `(load "file.lisp")` everything and it should generally just work. But of course, build systems are useful tools, so nonetheless ASDF exists and it's nice enough to the degree that nobody has built a better and more widespread common lisp build system.

Some good trivial examples are in the lisp cookbook:

https://lispcookbook.github.io/cl-cookbook/systems.html

No idea why you're being downvoted for asking a simple question about an acronym. From Wikipedia [1]:

> ASDF (Another System Definition Facility) is a package format and a build tool for Common Lisp libraries. It is analogous to tools such as Make and Ant.

Contemporary developers using more mainstream languages are likely more familiar with asdf [2], the "Multiple Runtime Version Manager".

[1] https://en.wikipedia.org/wiki/Another_System_Definition_Faci...

[2] https://asdf-vm.com/