Which term refers to the upper millstone?

The term that refers to the upper millstone is "mola." In ancient Roman and other Mediterranean cultures, the milling of grain was a critical process for producing flour, a staple in their diet. The millstone typically comprises two parts: the upper stone, known as the "mola," and the lower stone, which helps to grind the grain.

The "mola" rotates against the stationary lower stone, crushing the grain between them to produce flour. This setup is essential in the milling process, as the action of the upper stone directly affects the efficiency and quality of the milling.

In contrast, other terms mentioned in the choices refer to different concepts. "Meta" typically refers to a goal or limit, often used in contexts unrelated to milling. "Catillus" refers to a small dish or bowl, which does not pertain to the milling process. "Grana" refers to grains or seeds themselves, rather than the equipment used to process them. Thus, "mola" is the correct term for the upper millstone in this context.