Look at the Apple website. They list four iPad models. From right to left they are: The Mini, The iPad, the iPad Air, and the iPad Pro.
The Mini is small. It's 'mini', a smaller iPad. The iPad is, well, an iPad. The iPad Air is a lighter version of the iPad(?). The iPad Pro has a large screen version, plus they have more memory capacity choices than any other iPad, plus there are a lot of other things that the iPad Pro has that the others don't. The 'Pro' means size for the larger one, and size in capacity. The 'Pro' means external keyboard connectivity. The 'Pro' means more speakers. It's above and beyond the other models, in some cases way above. I'd call that 'Pro', for lack of a better word. Should they have called it 'Big'? Or 'Biggie'? Maybe 'Monster'? 'Pro' fits. I wouldn't buy a 2Tb iPad for just reading and listening/watching content. A graphics designer would probably consider that 'small'...