Select tongue and groove is a type of cladding which is what material/type of wood these sheds are constructed from. If you are not aware there are three types including overlap, shiplap and tongue and groove.
Tongue and groove cladding are usually 12mm thick and offer a sturdy construction. They will comfortably withstand the pressure of large items and the wood panels are specifically designed to reduce the chances of water penetrating the wood panels.
Select tongue and groove cladding is arguably the best value for money as although it is more expensive than overlap it has a sturdier build. Select tongue and groove is one of the most popular shed cladding choices.