What describes a contract in civil law with reciprocal obligations?

A synallagmatic contract is a type of agreement in civil law where the parties involved have mutual and reciprocal obligations towards each other. This means that each party is both a debtor and a creditor within the context of the agreement; one party's obligation is contingent upon the other party fulfilling their own obligation. For example, in a typical purchase agreement, the seller is obligated to deliver goods, while the buyer is obligated to pay for those goods. This mutual exchange characterizes the essence of a synallagmatic contract.

In contrast, a unilateral contract involves only one party undertaking an obligation without any reciprocal requirement from the other party. Nonapparent servitude and negative servitude pertain to rights related to land use and property restrictions rather than contractual relationships. Thus, these options do not embody the concept of reciprocal obligations as a synallagmatic contract does.