A collection of a same kind of entities is known as an Entity Set or entity type.
Example:
For the COLLEGE database defines earlier objects of concern are Students, Faculty, Course and departments. The sets of all the students' entities form a entity set STUDENT. Likewise collection of all the courses creates an entity set COURSE.
Entity sets require not be disjoint. For example - an entity may be part of the entity set STUDENT, the entity set FACULTY, and the entity set PERSON.