A Terminal Multiplexer is a software tool that allows users to manage multiple terminal sessions within a single window. It enables users to switch between different command-line interfaces easily, making it efficient for multitasking. Popular examples include tmux and screen, which provide features like session persistence, allowing users to detach and reattach to sessions without losing their work. These tools are particularly useful for remote server management, as they help maintain active sessions even if the network connection drops. By organizing multiple tasks in one interface, a terminal multiplexer enhances productivity and simplifies workflow for developers and system administrators.