Tmux Terminal Multiplexer
Tmux is a terminal multiplexer, it enables a number of terminals (or windows) to be accessed and controlled from a single terminal. Tmux is intended to be a simple, modern, BSD-licensed alternative to programs such as GNU screen. Tmux may be detached from a screen and continue running in the background, then later reattached.When Tmux is started it creates a new session with a single window and displays it on screen. A status line at the bottom of the screen shows information on the current session and is used to enter interactive commands.
A session is a single collection of pseudo terminals under the management of Tmux. Each session has one or more windows linked to it. A window occupies the entire screen and may be split into rectangular panes, each of which is a separate pseudo terminal. Any number of TMUX instances may connect to the same session, and any number of windows may be present in the same session. Once all sessions are killed, Tmux exits. Also checkout Tmux manual.