uniqueidentifier
Been around since sql7.
Massively long type - unique across dbs - possibly good for consolidating data from lots of diff sources.
16-byte binary value.
This is an example of a formatted GUID: B85E62C3-DC56-40C0-852A-49F759AC68FB.
NEWID() function used to get the guid.
DECLARE @GUID uniqueidentifier
SET @GUID = NEWID()
INSERT Item VALUES (@GUID,'Yak Hoof')