This document defines key concepts related to obligations under civil law, including:
1. It defines an obligation as a juridical necessity to give, do, or not do something, and discusses the meaning of juridical necessity.
2. It outlines the essential requisites of an obligation - a passive subject (debtor), active subject (creditor), object or prestation, and juridical tie.
3. It distinguishes between civil obligations, which can be enforced in courts, and natural obligations, which do not grant a right of action but can be fulfilled voluntarily.