tmux is a terminal multiplexer: it enables a number of terminals (or windows),
each running a separate program, to be created, accessed, and controlled from a
single screen. tmux may be detached from a screen and continue running in the
background, then later reattached. tmux is intended to be a modern,
BSD-licensed alternative to programs such as GNU screen.

tmux uses a client-server model. The server holds multiple sessions and each
window is a independent entity which may be freely linked to multiple sessions,
moved between sessions and otherwise manipulated. Each session may be attached
to (display and accept keyboard input from) multiple clients.