The generations determine the version of an iPad which would other wise be indistinguishable by name alone.
See Also
The redesigned iPad Air and new iPad Pro are available todayIs the iPad 10-2inch 10th Gen water-resistant?iPad 10.9 (10th gen.) - Technical SpecificationsiPad generations: all iPad modelsFor instance, Apple has made 4 different devices labeled as iPad Pro 12.9”. Starting in 2015.
Without te generation specification it would be very difficult to determine which device is being referenced.
Instead of calling it the 2015 iPad Pro 12.9”, its the First Generation iPad Pro 12.9”.
The 2017 Model is the second generation, the 2018 model is the third generation, and the 2020 model is the fourth generation.
