The Free On-line Dictionary of Computing (18 March 2015):
Tab Window Manager.
A window manager for the X Window System. Twm provides
titlebars, shaped windows, several forms of icon management,
user-defined macro functions, click-to-type and
pointer-driven keyboard focus, and user-specified key and
pointer button bindings. It can be extensively configured by
a startup file.
Twm was written by Tom LaStrange, Solbourne Computer; Jim
Fulton, MIT X Consortium; Steve Pitschke, Stardent
Computer; Keith Packard, MIT X Consortium; Dave Sternlicht,
MIT X Consortium; Dave Payne, Apple Computer.
An extended version, vtwm, provides a virtual desktop.