Okay, so let's say you have two pieces of metal that are really close together but not quite touching. When you send an electrical current through them, it creates a spark that jumps from one piece of metal to the other. That's called a spark gap.
Now, a triggered spark gap is a special kind of spark gap that you can control really precisely. Instead of just sending an electrical current through the gap to make it spark, you use another little spark or a pulse of light to make it spark exactly when you want it to.
This is really important for things like lasers or powerful electrical equipment, because you need the sparks to happen at exactly the right time for everything to work correctly. It's like pushing a button to turn on a light instead of just hoping that the light turns on when you flip the switch. It gives you more control over what happens, and that's a good thing!