MTG:diffrence between standard and type2?

My local card shop has standard and standard type 2 listed on difference days. What is the difference. I know type 2 is m11 then zendikar block with Alara etc rotating out. I know the oldest you can go in extended is planar chaos but, then my friend asked if this guild pact deck would be considered standard and the guy said yes. So what is the diffrence.