Yes, there is a big difference. Silicone is a rubbery glue. Epoxy is very strong, hard, and brittle glue. Epoxy comes in two tubes...one is a base, and one is a hardener. You mix those two and you get some real strong stuff.

I know you have been talking about clearing your headlights, and if you do that, and need extra glue to reseal them, use silcone, DO NOT use epoxy.

Silicone is generally used to seal something. Caulk, etc is silicone based.

Epoxy is great for something you want a very permanant fix on.