Elements of an obligation

Every obligation has four essential elements: an active subject; a passive subject; the prestation; and the legal tie.
The ACTIVE SUBJECT is the person who has the right or power to demand the performance or payment of the obligation. He is also called the obligee or the creditor.
The PASSIVE SUBJECT is the person bound to perform or to pay. He is the one against whom the obligation can be demanded. He is also called the obligor or the debtor.
The PRESTATION is the object of the contract. It is the conduct required to be observed by the debtor or the obligor. It may be an obligation to give, to do, or not to do.
The VINCULUM JURIS is also known as the juridical or legal Tie. Other authors call it the efficient cause. It is that which binds or connects the parties to the obligation. (De Leon) In other words, it is the legal relation between the debtor and the creditor (or obligor and obligee).
If you have an obligation to do something, it is your duty to do that thing. www.collinsdictionary.com/dictionary/english/legal-obligation.
In Black's Law Dictionary, obligation is a moral or legal duty to perform or not perform an act. Some legal scholars, including Fredrick Pollock, claim that obligation is another word for duty. The legal sense of obligation from early Roman law claims that obligations are the bond of vinculum juris, or legal necessity, between at least two individuals or parties. www.upcounsel.com/definition-of-obligation-in-law.
In Roman law, as with its successor, the civil law, theorists describe a fundamental feature of obligations (torts and contracts) by the legal tie, the vinculum juris that it creates between two persons. www.duhaime.org/LegalDictionary/V/VinculumJuris.aspx.
Vinculum iuris wÄ“n´kÅ«lÅ«m yÅ«´rÄ“s . vin´kyÅ«lum jÉœ´ris . n. “Chain of law.”(1) A reference to the binding nature of law.(2) A specific, legally binding obligation. www.oxfordreference.com/view/10.1093/acref/9780195369380.001.0001/acref-9780195369380-e-2107.