tmux is a terminal multiplexer that allows users to manage multiple terminal sessions within a single window. It enables users to split their terminal into multiple panes, each running different processes, making it easier to multitask and monitor various tasks simultaneously. With tmux, users can detach from a session and reattach later, preserving their work. This feature is particularly useful for remote server management, as it allows users to maintain their sessions even if their connection drops. Overall, tmux enhances productivity by providing a flexible and efficient way to handle terminal tasks.