Call of Duty 5: Triggers

Damage

Trigger that responds to taking damage. Damage trigger will trigger if a bullet intersects
them or if a projectile or grenade explodes inside the trigger.

Disk

Unknown

FriendlyChain

Forces any touching entity to be considered on the targeted friendly chain.

Hurt

Any entity that touches this will be hurt.
It does dmg points of damage each server frame.
Targeting the trigger will toggle its on / off state.

Look At

Requires a player to look at this trigger.

Multiple

Trigger that responds to players by default.
Can be triggered multiple times.

Once

Must be targeted at one or more entities.
Once triggered, this entity is destroyed.

Radius

Trigger that responds to players by default within radius.

Use

When activated will use its target.

Use Touch

When the player is touching and activated, the trigger will use its target

Sources: Treyarch's Wiki