The Wait Trigger option is available in the Wait for Binary Input robot control statement.
When a robot is connected to a conveyor like in the robot training layout. There we connect robot to two conveyors which have a sensor in the middle. When a pallet triggers the sensor, the conveyor signals to the robot.
The robot program waits for input from the conveyor. If we use Wait Trigger option, it means that the robot will actually wait for a change in the value. If the value is already 1 (true), the robot doesn't do (proceed in the program) anything yet, it will wait until the value actually changes to 1 (true).
If robot uses Wait Trigger with both conveyors at the same time, it is possible that the other sensor has already triggered while robot is still waiting for the first one to be triggered. In that case the second conveyor would not signal before the next signal trigger.