n. 1. The supervisor program or OS on a computer. 2. The entire computer system, including input/output devices, the supervisor program or OS, and possibly other software. 3. Any large-scale program. 4. Any method or algorithm. 5. `System hacker' one who hacks the system (in senses 1 and 2 only; for sense 3 one mentions the particular program e.g., `LISP hacker')