Aggregate is collection of objects that are bound together by a root entity
, which may be known as an aggregate root.
The aggregate root guarantees the consistency of changes being made within the Aggregate by forbidding external objects from holding references to its members.
When you drive a car, you do not have to worry about moving the wheels forward, making the engine combust with spark and fuel, etc.; you are simply driving the car. In this context, the car is an Aggregate of several other objects and serves as the Aggregate root to all of the other systems.
There might be more information for this subject on one of the following: