A more thorough explanation:

dimidium

Dimidium means half of something. It comes from the Latin word for "half".

• Dimidium unius libratae means half a pound.
• If you have a pizza and you cut it in half, each half is a dimidium of the whole pizza.

The examples show that dimidium refers to a half of something, whether it's a weight or a pizza. It's a way to describe a portion that is exactly half of the whole.