This document provides an overview of key concepts in civil law related to sales, including definitions of sale, contract to sell, conditional sale, barter, dation in payment, and price. It defines a sale as a contract whereby one party transfers ownership of a determinate thing in exchange for a certain price paid by the other party. A contract to sell differs in that ownership is reserved by the seller until full payment of the purchase price. The document outlines essential elements, natural elements, and accidental elements of a sale, as well as characteristics such as being principal, consensual, bilateral, and onerous. It also distinguishes between a sale and related contracts such as agency to sell, contract for piece of work, and