Threshold
The raised strip or ramp at the base of a shower entry that helps contain water inside the shower area, distinct from the door seal itself.
A threshold is part of the shower base or pan, not the door — it's the small raised lip you step over entering the shower. It works together with (not instead of) a bottom sweep: the sweep seals the door-to-glass gap, the threshold contains water that gets past it.
On curbless/barrier-free showers there is no threshold at all, which puts more of the sealing job on the door sweep and on the floor slope — a common reason curbless showers need a longer, more effective sweep than a standard curbed shower.