ob·li·ga·tion 
(ŏb′lĭ-gāshən)
(ŏb′lĭ-gāshən)n.
1.
a. A social, legal, or moral requirement, such as a duty, contract, or promise, that compels one to follow or avoid a particular course of action: Are you able to meet your obligations? I have an obligation to attend their wedding.
b. The constraining power of a promise, contract, law, or sense of duty: I felt no obligation to offer my advice.
c. Law A document in which a person binds himself or herself to undertake or refrain from doing a particular act.
d. A debt instrument, such as a loan, mortgage, or bond.
2. The state, fact, or feeling of being indebted to another for a special service or favor received: If they invite us, aren't we under obligation to invite them in return?
ob′li·gation·al adj.