SECD is an extremely simple *(Abstract VM) for functional programming, including the use of _(Lisp). It's a very old concept, dating from the mid-1960's.

The most general information and set of implementations seem to be _(SECD Mania|http://skelet.ludost.net), although more references to it can be found.

See also <a href="http://www.cs.utexas.edu/users/boyer/ftp/nqthm/trsecd/trsecd.html">The Tail Recursive SECD Machine</a>.