A cup is a flared container with a concave shape. It can be made of glass (known as a "watch glass") or plastic.
There are different shapes and sizes.
A cup is used to weigh small amounts of solids (powder or small pieces). It is usually tared beforehand, before being placed on the scale. The solid is then deposited in the cup so that it can be weighed.
Once the weighing is completed, the solid is generally transferred to a container (e.g. a volumetric flask) using a funnel. It is necessary to rinse the cup with the liquid used to make the solution (water or solvent, as appropriate) to avoid losses on the cup (e.g. using a wash bottle).
read the sheet on A guide to weighing
Illustration of weighing cups made of plastic.