choke-point

Choke points are narrow passages that restrict mass movement from the chokepoint ends: the RTS equivalent is a ramp/bridge.
Units/monsters without ranged attacks are forced to come through the chokepoint in very few numbers, allowing defending entities to prepare defenses or cast skills repeatedly.
Units with ranged attacks are often obstructed from attacking beyond the chokepoint entrance, which reduces the damage of swarming the defending side.

Tactics in RTS:
Breakthrough through the chokepoint requires:
1.Bypassing the chokepoint from air or other sides.
2.Moving units through gaps without attacking,"scaling the chokepoint" and then swarming the enemy.
Defense:
1.Building blocking/defense structures to minimize gaps.
2.Surrounding the chokepoint with units: "focus fire" area with center being the choke point.

Tactics in RPGs:
1.Players holding the chokepoint: "Blockers"/"tankers" stop monster flow, by attacking/stunning nearest monsters.
2.Players with ranged attacks or AoE skills use their firepower on monsters beyond the chokepoint.