What is the meaning of keister?

noun

• 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: buttocks, nates, arse, butt, backside, bum, buns, can, fundament, hindquarters, hind end, posterior, prat, rear, rear end, rump, stern, seat, tail, tail end, tooshie, tush, bottom, behind, derriere, fanny, ass