Dependency is where one object must know about another.
In a simple dependency relationship all we know is that one object has knowledge of another. For example, in C++, if one class requires the inclusions of the header for another, that establishes a dependency.

Association: Models a semantic connection among classes

Aggregation: A special form of association that models a whole-part relationship between an aggregate (the whole) and its parts

Composition:A form of aggregation with strong ownership and coincident lifetimes(The parts cannot survive the whole/aggregate)

In an association, the state of the object depends on another object.
In an association we say that, as part of understanding the state of one object, you must understand the relationship with the second object. There are many types of association which model real-world relationships such as owns (John owns this car), works for(Pete works for Bill) and so forth.
In an association the two objects have a strong connection but neither one is a part of the other. The relationship is stronger than dependency; there is an association affecting both sides of the relationship.

Objects are ofter made up of other objects. Cars are made up of steering wheels, engines,transmissions and so forth. Each of these components may be an object in its own right. The special association of a car to its component parts is known as aggregation.