out keyword causes arguments to be passed by reference only difference is that out parameters doesn\’t require initialization like ref parameter and out parameter must assigned/initialize inside method.

Points to remeber

• The ref and out keywords cause different run-time behaviour, they are not considered part of the method signature at compile time. You can not overload method by ref and out.

class Example
{
    // Compiler error CS0663: "Cannot define overloaded  
    // methods that differ only on ref and out". 
    public void Method1(out int i) {
        i = 1;
    }
    public void Method1(ref int i) { }
}

• Property, indexers, dynamic types can not be passed as ref or out parameter.

• Async methods, which you define by using the async modifier can not use ref or out.
• Iterator methods, which include a yield return or yield break statement can not use ref or out.