Entities, Relationships, and Attributes
Definition of an Entity
An entity is a database object that represents a thing in the real world. Entities are expressed as nouns.
Entities can be concrete, like buildings and employees or they can be more abstract things like departments and accounts.
Loosely speaking, an entity corresponds to a relation in relational theory. When a relation is made physical, it is normally referred to as a table, though the term is also used to describe physical as well as conceptual tables.