hd: A BDSM abbreviation for humiliation and discipline. Also short for High Definition
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.
pornstar: As a video genre, it involves famous stars of the porn industry.