TECO (for Text Editor and COrrector is a programmable, character-oriented text editor developed in 1962 by MIT student Dan Murphy for working with punched paper tape (“TECO” originally stood for Tape Editor and Corrector) on a DEC PDP-1.

The original version of Emacs (the version available on twenex.org) was programmed in TECO macro language (“Emacs” stands for Editor macros).

There is a TECO survival guide on the SDF tutorials page.