What is Obligatio?

Legal Definition
Lat. In Roman law. The legal relation existing between two certain persons whereby one (the creditor) is authorized to demand of the other (the debtor) a certain performance which has a money value. In this sense obligatio signifies not only the duty of the debtor, but also the right of the creditor. The fact establishing such claim and debt, as also the instrument evidencing it, is termed "obligation." Mackeld. Rom. Law, § 360. That legal relation subsisting between two persons by which one is bound to the other for a certain performance. The passive relation sustained by the debtor to the creditor is likewise called an "obligation." Sometimes, also, the term "obligatio" is used for the causa obligationis, and the contract itself is designated an "obligation." There are passages in which even the document which affords the proof of a contract is called an "obligation." Such applications, however, are but a loose extension of the tenn, which, according to its true idea, is only properly employed when it is used to denote the debt relationship, in its totality, active and passive, subsisting between the creditor and the debtor, Tomk. & J. Mod. Rom. Law, 3OL

Obligations, in the civil law, are of the several descriptions enumerated below.

Obligatio owitis is an obligation enforceable by action, whether it derives its origin from jus cwile, as the obligation engendered by formal contracts or the obligation enforceable by bilaterally penal suits, or from such portion of the jus gentium as had been completely nainralized in the civil Jaw and protected by nil its remedies, such as the obligation engendered by formless contracts. '

Obligatio naturalis is an obligation not immediately enforceable by action, or an obligation imposed by that portion of the jus gentium which is only imperfectly recognized by civil law.

Obligatio ex contractu, an obligation arising from contract, or an antecedent jus in personam. In this there are two stages.—first, a primary or sanctioned persona] right antecedent to wrong, and, afterwanis, a secondary or sanctioning personal right consequent on a wrong. Poste's Gaius' Inst. 359.

Obligatio ex delicto, an obligation founded on wrong or tort, or arising from the invasion of a jus in rem. In this there is the second stage, a secondary or sanctioning personal right consequent on a wrong, but the first stage is not a personal right, (jus in personam,) but a reni right, (jus in rem,) whether a primordial right, right of status, or of property. Poste's Gams' Inst. 359.

Obligationes ex delicto are obligations arising from the commission of a wrongful injury to the person or property of another. "Delictum," is not exactly synonymous with "tort," for, while it includes most of the wrongs known to the common law as torts, it is also wide enough to cover some offenses (such as theft and robbery) primarily injurious to the individual, but now only punished as crimes. Such acts gave rise to an obligatio, which consisted in the liability to pay damages.

Obligationes quasi ex contractu. Often persons who have not contracted with each other, under a certain state of facts, are regarded by the Roman law as if they had actually concluded a convention between themselves. The legal relation which then takes place between these persons, which has always a similarity to a contract obligation, is therefore termed "obligatio quasi ex contractu." Such a relation arises from the conducting of affairs without authority, (negotiorum gestio;) from the management or property that is in common when the commuhity arose from casualty, (communis incidens;) from the payment of what was not due, (solutio indebiti;) from tutorship and curatorship; and from taking possession of an inheritance. Mackeld. Rom. Law, § 491.

Obligationes quasi ex delicto. This class embraces all toris not coming under the denomination of "delicta" and not having a special form of action provided for them by law. They differed widely in character, and at common law would in some cases give rise to an action on the case; in others to an action on an implied contract. Ort. Inst. §§ 1781-1792.
-- Black's Law Dictionary
Legal Definition
An obligation.
-- Ballentine's Law Dictionary