Definition of "Obligation" :

noun: the social force that binds you to the courses of action demanded by that force

"Every right implies a responsibility; every opportunity, an obligation; every possession, a duty."

noun: a legal agreement specifying a payment or action and the penalty for failure to comply

noun: a written promise to repay a debt

noun: a personal relation in which one is indebted for a service or favor

noun: the state of being obligated to do or pay something

"He is under an obligation to finish the job."