Superscalar
Beginner
A processor that can start more than one step of a program in the same tick of its clock.
Novice
A processor that fetches, issues and finishes several instructions per clock cycle, using several execution units side by side. A 4-wide core can start up to four instructions each cycle.
Expert
Width applies separately to fetch, decode, rename, issue and commit; sustained IPC is far below peak width because of dependences, mispredictions and misses. Wider machines need quadratically more bypass and wakeup logic.
Explained in Branch prediction and out-of-order execution (Architectures).
See also: Out-of-order execution.