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.
anal: Anal insertion with finger, penis, or toy.
anal sex: Sex involving the insertion of the penis (or some other body part/object such as a dildo) into the anus