Association

There are two basic types of association
Aggregation & Containment

the best word to express it would be custome reference types

e.g
Class Engine { public int HoursePower; }

class Auto { public Engine Engine; }

Main Class

{
PSVM {
Auto myCar=new Auto();
myCar.Engine=V6;
Console.writeline(myCar.Engine.HoursePower.toString());
}

relation between mycar and Engine is Aggreation