passing parameters in C#

Question

What i knew about 'out' parameter in c# is that if we want to  return more than one from a single routine. But we can use  'ref'  to return more than one from a single  routine.Ofcourse  ' out ' parameter also passed as  reference variable. Then what is the need of  'OUT' ? where exactly we need 'out'? Please explain with real time situation.