A mid-sized computer system traditionally used for scientific, engineering, or business applications. They typically occupied a rack or a few cabinets, offering significant processing power and multi-user capabilities without the massive infrastructure required by mainframes. The category largely faded as microprocessors grew powerful enough to handle the same workloads.
Heard on the job
We used to run the entire test floor off a single PDP-11 minicomputer before we switched to distributed PCs.