What is the difference between Association and Aggregation?

Question

I am very confused about the differences between Associations and Aggregations as both are almost the same, and both objects in the relation can exist without the other.

There is a post on stack overflow trying to explain this

Association - I have a relationship with an object. Foo uses Bar

public class Foo {         
    private Bar bar;
};

Aggregation - I have an object which I've borrowed from someone else. When Foo dies, Bar may live on.

public class Foo { 
    private Bar bar; 
    Foo(Bar bar) { 
       this.bar = bar; 
    }
}

source {https://stackoverflow.com/a/10394722}

Both looks almost identical to me, can someone explain when is a relation an association and when is it an aggregation.