More generally, in any group, or even any monoid, the group operation is often called ‘multiplication’ and written as juxtaposition, and then the identity element is called one and written as . As a consequence, in any ring, or more generally any rig, the two binary operations are called ‘addition’ and ‘multiplication’, and the identity for multiplication is called one.
Categorifying this idea, in any monoidal category the monoidal unit may be called one. This is especially true in the case of a cartesian monoidal category, that is a category with (at least finitary) products. In this case the terminal object, which serves as the identity for products, is often called one:
All these ideas can be, and have been, categorified further.