Representations

To be precise you would say that XII, ///// ///// //, and 12 are different ways to represent the same number.

There are many ways to represent that number. The number is always the same number. But a variety of ink marks (or pencil marks, or chalk smudges, or characters on a computer monitor) can represent it. In normal conversation and in writing "number" often means the representation of a number. For example, you might call

12

a "number". It would be tedious to call it "an instance of the representation of a particular number using Arabic digits with the decimal system." But that is what it is.

Computer Science is concerned with using patterns of bits to represent things. It is important to be clear about the difference between the thing, and a representation of the thing. For example, an integer may be represented using a bit pattern in computer memory. (There are many different ways to do this.) The integer is conceptual. The bit pattern is only a representation of the concept.