Assignment operator (=) in argument of Method Definition

See below method definition.

What is it called in C# where t开发者_高级运维he equals sign is in method parameter.

Does it default method parameter initialization??

public List<Iabc> MyMethod(out List<Ixyz> faces, Type typeXYZ = null, int flag = -1)
{
    //...
    //...   
}

NOTE: Here Iabc and Ixyz are any Interfaces.

They're called optional (or named) arguments. MSDN usually has these things explained pretty well:

Named and Optional Arguments (C# Programming Guide)

When using named arguments, be aware that changing argument names will break code. (where named parameters are used)

Also, remember that the default value is actually stored in the call site meaning that if you at some later point change the default value, code that is calling the method and was compiled before the change, will still use the old value. it might not matter in all situations but its something to be aware of.

That's an optional argument in C# 4.0