From FSDeveloper Wiki
Generic Trigger Properties are integral, and applicable, to all trigger types, (except where noted).
Airport Landing Trigger fires when the user's aircraft (not AI controlled aircraft) lands on a runway.
Area Landing Trigger fires when the user's aircraft (not AI controlled aircraft) lands on one in a specified list of areas.
Menu Prompt Trigger creates a menu of options for the user. For some missions this can be as simple as the option to continue, and the option to turn back.
Parking Trigger fires when the user has reached the parking spot assigned by the ATC at the airport specified.
Property Triggers fire when one or more conditions are met. These conditions can be based on aircraft speed, altitude, failure of components, or a whole host of other simulation variables.
Proximity Trigger fires when the specified object, usually the users aircraft, enters a given box.
Timer Trigger fires when the given number of seconds has elapsed.