Multi-user

From Freepedia

Multi-user operating systems allow multiple users to utilize the computer and run programs at the same time. All time-sharing systems are multi-user systems, but most batch processing systems for mainframes were too, to avoid leaving the expensive CPU idle while it waited for I/O operations to complete.

The most obvious example is a Unix server where multiple remote users have access (via Telnet) to the Unix shell prompt at the same time.

The opposite term single-user is most commonly used when talking about an Operating System being useable only by one person at a time, or in reference to a single-user software license agreement.