Tmux as defined in Wikipedia is a terminal multiplexer for Unix-like operating systems. It allows multiple terminal sessions to be accessed simultaneously in a single window. It is useful for running more than one command-line program at the same time.
Here is my cheat sheet for tmux and other stuff I will learn about it
tmux - starts the session tmux ls #list:sessions - lists the active running tmux sessions. tmux new -s session_name - starts a new tmux session.