TECO

 TECO (tee'koe) [acronym for Text Editor and COrrector] 1. n. A text
       editor developed at MIT, and modified by just about everybody. If all
       the dialects are included, TECO might well be the single most prolific
       editor in use. Noted for its powerful pseudo-programming features and
       its incredibly hairy syntax. 2. v. To edit using the TECO editor in
       one of its infinite forms; sometimes used to mean "to edit"
       even when not using TECO! Usage: rare at SAIL, where most people
       wouldn't touch TECO with a TENEX pole. [Historical note: DEC grabbed
       an ancient version of MIT TECO many years ago when it was still a
       TTY-oriented editor. By now, TECO at MIT is highly display-oriented
       and is actually a language for writing editors, rather than an editor.
       Meanwhile, the outside world's various versions of TECO remain almost
       the same as the MIT version of ten years ago. DEC recently tried to
       discourage its use, but an underground movement of sorts kept it
       alive.] [Since this note was written I found out that DEC tried to
       force their hackers by administrative decision to use a hacked up and
       generally lobotomized version of SOS instead of TECO, and they
       revolted. - MRC]