A "Membership Relation" is a concept in database management that defines how entities are related to one another within a database. It typically involves a set of members that belong to a specific group or category, allowing for organized data retrieval and management. For example, in a database for a library, the membership relation could include members who have access to various books and resources. In relational databases, membership relations are often represented through tables, where each row corresponds to a member and their attributes. This structure helps maintain data integrity and supports efficient queries. For instance, a gym might have a membership relation that tracks members, their membership types, and expiration dates, facilitating easy management of member information.