What is an Extension of entity type?

An extension of an entity type is specified as a collection of entities of a particular entity type that are grouped into an entity set.

In the context of a database management system (DBMS), an extension of an entity type refers to the instances or occurrences of that entity type.

For example, if you have an entity type “Employee,” the extension of this entity type would be the actual employees in a company database, each representing a distinct instance of the “Employee” entity type.

So, the correct answer would be: Instances or occurrences of an entity type.