In its default configuration, the Lisp reader translates Lisp source text into an efficient list representation of the program at the time the program is read . Thus the compiled code is interpreted by the emulator. In short, at some level, all software on every machine is interpreted. ANSI Common Lisp requires that each implementation provide a compiler which obeys certain rules. The standard recognizes the different possibilities for implementation.
Some systems do both.
All implementation must at least perform some minimal compilation such as expanding macros so that they do not need to be expanded again at run-time.