PDO stands for Protected Designation of Origin I think - its the EU stamp that means that a certain product is unique and special to a locality and has a real quality to it which depends on stuff like local ingredients and water and animals diets.
So altho I have Shetland sheep, 'Shetland lamb' now has a PDO, which means I have to be very clear if I sold any to make sure the buyer knows they are not getting 'Shetland Lamb' (which can now only be from Shetland) but rather lamb from a Shetland sheep.
It is a bit problematic, this giving of PDOs to a product which shares its name with a breed of animal!
Other PDOs include things like Arbroath Smokies, Dorset Vinny cheese etc.