What is entity in Relational Database Management System (RDBMS)?

An entity represents a real world object about which we want to store data in database. Entities are distinguishable from other pbjects. Some entities are tangible such as book to which one can touch and feel. Some entities are abstract and cannot be touched or felt. For example, a student grade in courses.

Let us take examples of entity.
Tangible entities
Ex. Employee — Employee is a person, and we can feel the physical existence of a person.
Ex. Student — Student is a person, and we can feel the physical existence of a person.
Ex. Product Product like pencil or book are also tangible objects and hence we can feel them.
Intangible or abstract entities
Ex. Student grade — Grade is abstract because we cannot touch it. We can describe it.
Ex. Class schedule — This is an abstract entity as we can describe the schedule but cannot touch it or feel its physical existence.
Ex. Concert event — Event can be described but cannot be felt.

In short when an entity is described, it conveys information about it regardless of it being concrete or abstract. Each entity can be described by its characteristics. It is this description we save in a database. There is another term that we use in relation to the entity Entity Set. The word Entity Set refers to the set of similar entities. For example, the set of all products in inventory, set of all customers, and set of all suppliers. In common practice we use the entity to mean entity set.

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