verified amateur: As many videos are branded "amateur", which can also mean "low budget professional" lots of sites offer a "certified amateurs" category with only "real" amateurs.
amateur: Like in sports, amateur porn features individuals who are not professional porn stars. It features ordinary individuals partaking in every day sexual acts. Girl/boy next door, wives/husbands, girlfriends/boyfriends. Sometimes real amateurs but quite often professional models just pretending.
college: College porn is a genre that focus on students. It features young performers an a college lifestyle: dorms, frats, sororities...
hardcore: Explicit movies or videos that show genitals, especially an erect penis, and often include penetration. In this meaning, "hardcore" is the exact opposite of SOFTCORE. But for many porn videos, it just means an intense or dangerous sexual activity.