Hi! I've seen a lot of projects that say -the title- AMV or PMV or OC
What do those stand for?

AMV is an Animated Music Video and a PMV is a Picture Music Video. PMVs aren't animated and just have a backdrop or picture with the music playing, but the AMVs have moving sprites or effects along with the music. OC means “original character”. Hope this helps!

Thank you so much!

You're welcome!