The term "cupping" most likely originated as a description for a specific type of tire wear pattern due to its physical description, i.e., a hemispherical protrusion.
It is a fairly common occurrence on tires in general and, specifically, on motorcycle tires. One theory is that front tires on motorcycles are especially susceptible to cupping because of the light load sustained on the front tire; consequently, the front tire has a tendency to bounce (relatively speaking) resulting in irregular wear patterns.
From:
https://www.dunlopmotorcycle.com/infocenter_faq.asp?id=9
"You may not be able to entirely avoid cupping. Tire cupping or irregular wear is a somewhat common occurrence on all vehicles. On a four-wheel vehicle, you are advised to rotate your tires periodically to even out wear. Unfortunately, you do not have this luxury with a motorcycle because front and rear tires, unlike those on a four-wheel vehicle, are not interchangeable. However, there are steps that can be taken to minimize cupping and uneven wear on a motorcycle:
1. Maintain your motorcycle and particularly your front forks and suspension.
2. Avoid hard braking whenever possible. Braking causes the tire to grab and wear in one direction. When braking is applied to the front tire, the load transfer over-flexes the tire and increases the tendency for cupping and uneven wear.
3. Maintain your tire pressures. Underinflation or overinflation in motorcycle tires are significant causes of cupping and uneven wear, particularly in association with hard braking and/or trailer use."
