means A duty or commitment you're bound to fulfill, whether by promise, law, contract, or conscience.

from From Latin 'obligatio,' a noun built on 'obligare' — 'to bind around, to tie up' — from 'ob-' (toward, around) plus 'ligare' (to bind), the same root that knots through 'ligature' and 'ally.' So at heart an obligation is literally something that binds you; the word arrived in English through Old French 'obligacion' in the medieval period, already carrying its sense of a legal or moral tie.