In civil law, consideration is not a requirement for a valid and enforceable contract. Thus, the term is used to distinguish those contracts where reciprocal obligation exists from those where they do not.
§1390 of the 2008 edition of Quebec's Civil Code:
"A contract is synallagmatic, or bilateral, when the parties obligate themselves reciprocally, each to the other, so that the obligation of one party is correlative to the obligation of the other. When one party obligates himself to the other without any obligation on the part of the latter, the contract is unilateral."
Almost identically, the 2008 Louisiana Civil Code provides, at §1908:
"A contract is bilateral, or synallagmatic, when the parties obligate themselves reciprocally, so that the obligation of each party is correlative to the obligation of the other."
A contract of sale is a classic example, where one party provides money and the other, goods or services; or an employment contract, where the employer provides money as salary or wages, and the employee, specified services.
A gift is not a synallagmatic contract.