Final answer:
E.R. stands for Entity-Relationship in a relational database. It is a logical model used to represent the relationships between different entities in a database.
Step-by-step explanation:
E.R. stands for Entity-Relationship in a relational database. It is a logical model used to represent the relationships between different entities, such as tables or objects, in a database. The E.R. model uses various symbols and notations to depict these relationships, such as lines, diamonds, and rectangles.