Common Lisp has a standard, which was initially published in 1994 as an ANSI standard.
The Common Lisp HyperSpec, short CLHS, provided by LispWorks is an often used HTML documentation, which is derived from the standard document. The HyperSpec can also be downloaded and locally used.
Common Lisp development environments usually allow lookup of the HyperSpec documentation for Lisp symbols.
See also: cliki on CLHS