The term 'millesimus' translates to 'one-thousandth' in English, and it is an ordinal number used to indicate a position in a sequence, specifically the thousandth element. This term is part of a broader system of ordinal numbers in Latin, which provide a way to describe the order or rank of items in a list or series. Understanding 'millesimus' helps to grasp how numbers are articulated in Latin and their grammatical applications in various contexts.