Catapult = energy comes from tension. Trebuchet = energy comes from gravity pulling on a counterweight
You can only build up so much tension in ropes and wood so the weight of what can be thrown is limited. With a trebuchet you can throw heavier objects by increasing the weight of the counterweight and length of the throwing arm
These are both examples of catapults, broadly, siege engines that use stored energy to make big projectile go over there real good.
What people tend to refer to when they say “catapult” is a mangonel or onager, and go on to imply that the trebuchet is not a catapult. It is a catapult, just a different kind. Much like we have cars, which are vehicles, but we also have trucks, which are also vehicles.
