What is an ER diagram and what are its components?

An Entity-Relationship (ER) diagram is a visual representation of database structure showing entities (tables), their attributes (columns), and relationships between them. Components: Rectangles represent entities, Ovals represent attributes, Diamonds represent relationships, Lines connect entities through relationships. Relationship cardinalities show one-to-one (1:1), one-to-many (1:N), or many-to-many (M:N). ER diagrams help in database design before implementation.