THICK: A stamp with most of the back thinned except for one small area of normal paper.
Seriously there are no hard and fast rules about the SUBJECTIVELY define general terms. Just understand defects are always small for the seller and huge for the buyer.
Scott shows examples of how hinged stamps are and those are ignored. Why would they add photos of thins also to be ignored.
Oh, the stamp with a thick? I paid a dollar for it and gave it to the now ex-wife. From the from it would be described as a Mint US C3 100J with full OG and NH on the thick. Being such a huge jumbo is likely why it never found its way on an envelope as postage even in its condition.