http://www.c-sharpcorner.com/UploadFile/7c64d7/all-about-ref-and-out-type-parameters/

ref and out are the output parameters that returns the output of the method to the program. the difference between ref and out is: when ref is used, the variables we are substituting while calling a method must be initialized but optional in case of out.

http://www.codeproject.com/Tips/792490/ref-and-out-Parameters-in-Csharp