The term "overwatch" is when a unit can shoot/attack an enemy unit during the turn of the player controlling the enemy unit.
The following criteria need to be met to enable overwatch:-
- The overwatch unit must have ended their turn with at least half their APs unspent.
- There must not be a friendly unit adjacent and visible to the overwatch unit.
- The overwatch unit must have an appropriate weapon.
- The enemy unit must not have been visible to the overwatch unit at the end of the previous turn.