What is the meaning of buttocks?

noun

• Either of the two large fleshy masses of muscular tissue that form the human rump.
  • synonyms: buttock, cheek
• The fleshy part of the human body that you sit on.
  • usage: "he deserves a good kick in the butt"; "are you going to sit on your fanny and do nothing"
  • synonyms: nates, arse, butt, backside, bum, buns, can, fundament, hindquarters, hind end, keister, posterior, prat, rear, rear end, rump, stern, seat, tail, tail end, tooshie, tush, bottom, behind, derriere, fanny, ass