An entity–relationship model describes interrelated things of interest in a specific domain of knowledge. Entity Relationship Diagram, also known as ERD, ER Diagram or ER model, is a type of structural diagram for use in database design. An Entity Relationship Diagram (ERD) is a snapshot of data structures. An entity relationship diagram (ERD) shows the relationships of entity sets stored in a database. An entity relationship diagram (ERD), also known as an entity relationship model, is a graphical representation that depicts relationships among people, objects,. What is an ER diagram? An Entity Relationship (ER) Diagram is a type of flowchart that illustrates how “entities” such as people, objects or concepts relate to each.