Toggle buttons have a 'true' state and a 'false' state. When the button is clicked once, it latches on to the opposite state. That is, if the button is off and then clicked, it will latch on and vice versa. You can think of a toggle button like a light switch - when it is on, the light is on and when it is off, the light is off.

Like toggle buttons, momentary buttons have a 'true' state and a 'false' state. However, with a momentary button, the button is only on while it is held down and if it is not held down, it is off. A good use case for a momentary button would be a push-to-talk button on a microphone. While the button is held down, the mic is unmuted. When it is not held down, the mic is muted. Another good example of momentary buttons are the pan, tilt, and zoom controls on QSC PTZ cameras.

Trigger buttons are unlike toggle and momentary buttons in that they have NO state. They should be thought of as a means of triggering an event. 

A good example of trigger buttons would be something like snapshot load or save buttons. They are used to trigger a preset (or save a preset), so there is no need for there to be state associated with the button. 

One thing to keep in mind is that if you try to wire a trigger button to a button or control that DOES have state, nothing will happen, because the trigger cannot pass a state. 

For example, you cannot wire a trigger to an LED and expect the LED to turn on when the trigger is pressed. The trigger cannot pass an 'On' state to the LED.