Text Editor and Corrector

TECO (pronounced /tee'koh/; originally an acronym for [paper] Tape Editor and COrrector, but later Text Editor and COrrector) is a text editor originally developed at the Massachusetts Institute of Technology (MIT) in the 1960s, after which it was modified by 'just about everybody'. With all the dialects included, TECO may have been the most prolific editor in use before the vi editor (later included with the UNIX operating system), and before the Emacs editor, to which TECO was directly ancestral ('Emacs' originally stood for Editing MACroS running on TECO).
See more at Wikipedia.org...