Well, I have a Line 6 Spider IV 15 and it has 4 buttons:
Clean, Crunch, Metal ans Insane.
Clean has no effects, so it sounds like a normal guitar. Now, if I choose Crunch, there's a little more Gain, Metal has more gain and Insane has the most.
So Crunch is an effect where you have a little gain. (That's the best way I can explain it, hope it helped)