[gambit-list] define-type and define-record-type

I keep seeing references to those in code samples all over gambit written code. What do they do exactly? I think I know, but they seem to take a plethora of keywords as well constructor:, extender:, implementer: etc. Sorry about the noise, Pavel P.S. These are somewhat documented on the wiki, but most of the keywords they take are undocumented.