A flush cut is the finishing cut made with the nipper’s flat face laid against the part, shearing the remaining nub level with the surface. It is the second half of two-stage cutting — the first cut relieves stress out on the gate, the flush cut removes what is left.
With a sharp single-blade nipper, a good flush cut leaves a mark you can barely feel; a few passes of fine sanding finish the job. Cheap double-bevel blades tend to dig or pinch instead of shearing flat.
See it in context in our nippers & cutting tools guides, or explore the tools hands-on in The Bench.