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.
hd: A BDSM abbreviation for humiliation and discipline. Also short for High Definition
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.