Lisp is a programming language. It is named after the collapsed phrase List Processing.
If you have programmed before and would like to see a little bit of how Lisp works and is different from other programming languages, you can get an overview.
Because Lisp itself is, technically, just seven operators, to become a useful language, much more needs to be implemented atop it. Common Lisp and Scheme are two such designs to create a useful programming language.
Common Lisp is an ANSI standard, and features an extensive array of library functions. It is the more widely used of the two.
Scheme is designed in a minimalistic fashion, with a very small amount of built in functions. This is probably true, but Scheme lacks many of the time-saving built-in functions of Common Lisp.
Emacs Lisp is an implementation of Lisp in Emacs.
newLISP is a Lisp-like, general-purpose scripting language
Lush - lisp-like object-oriented programming language