the.com/posterior

means The buttocks — or more formally, the part of anything situated behind or at the rear; in logic and statistics, the belief or probability you hold after accounting for new evidence.

from Straight from Latin posterior, 'latter' or 'coming after,' itself the comparative form of posterus ('following, next'), rooted in post ('after, behind'). English borrowed it in the 1500s for things literally positioned behind, and the polite-euphemism sense for 'buttocks' followed soon after — because calling someone's backside their 'posterior' let you discuss anatomy while sounding like you were discussing geometry. The statistical sense (posterior probability, the updated belief that comes 'after' new data) is a much later, 20th-century technical borrowing of the same core Latin idea: whatever comes after.