An entity-relationship model is a diagrammatic approach to a DATABASE design where real-world objects are represented as ENTITIES and relationships between them are mentioned.

• Entity: An entity is defined as a real-world object having attributes that represent characteristics of that particular object. For example, a student, an employee, or a teacher represents an entity.
• Entity Type: An entity type is defined as a collection of entities that have the same attributes. One or more related tables in a database represent an entity type. Entity type or attributes can be understood as a characteristic which uniquely identifies the entity.  For example, a student represents an entity that has attributes such as student_id, student_name, etc.
• Entity SET: An entity set can be defined as a set of all the entities PRESENT in a specific entity type in a database. For example, a set of all the STUDENTS, employees, teachers, etc. represent an entity set.