Plain English Meaning
Two aircraft using crossing runways or paths at the same moment, made safe by having one of them stop before the crossing point.
Full Definition
In the LAHSO context, simultaneous operations are air traffic control procedures that allow two or more aircraft to use intersecting runways, or a runway and an intersecting taxiway, at the same time, with one aircraft required to land and stop short of the intersection so the other aircraft can land, take off, or cross safely.
Context Anchor
Seen in Land and Hold Short Operations discussions, where a landing pilot may be asked to stop before a specific point so another aircraft operation can continue at the same time.