mature: Porn niche involving performer(s) over the age of 40. A popular emerging sub-niche of the mature niche are MILFs or Sexy Moms.
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.
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.