Choke point
Also said as Chokepoint, Bottleneck
A narrow place every attacker must pass through, so only a few of them can fight at once. Numbers stop counting: the side in the narrow place fights the front rank, not the army.
It makes a small force strong, which gives defenders something to hold and attackers a problem to solve. A map with no alternative to one becomes a stalemate that nobody enjoys.
Say it
“Attackers lose every round at the bridge. It is a two-wide choke with no way round, so widen it to five or add a second route under it.”
Where you’ve seen it
StarCraft bases sit at the top of a narrow ramp, so Terran players wall it off with buildings early on, and a handful of units can hold the entrance against far more.
Not to be confused with funnelling
Funnelling steers people, usually without their noticing. A choke point decides a fight, and everyone involved knows it is there.