Method Object:GetGUID [-] [+]
Returns the GUID of the Object.
GUID is an unique identifier for the object.
However on MaNGOS and cMangos creatures and gameobjects inside different maps can share the same GUID but not on the same map.
On TrinityCore this value is unique across all maps
guid = Object:GetGUID()
Valid numbers: integers from 0 to 18,446,744,073,709,551,615.