Instruction window
Beginner
How many steps of the program a processor can hold at once while it looks for ones that are ready to run.
Novice
The set of instructions an out-of-order core has fetched but not yet retired, from which it picks ready ones to run. A bigger window can find more independent work, for example while a load waits on memory.
Expert
Bounded by the ROB and by every other in-flight resource (physical registers, issue-queue entries, load and store queue entries). To keep issuing W per cycle through a latency L takes about W·L entries.
Explained in Branch prediction and out-of-order execution (Architectures).
See also: Reorder buffer (ROB), Out-of-order execution.