Decimal notation describes numbers using the digits 1 through 10. Binary notation describes them using just two digits, 1 and 0, where each bit in a string represents a power of 2. The right-most bit ...
PC Magazine

binary numbers

In the computer, all data are represented as binary digits (bits), and eight binary digits make up one byte. For example, the upper case letter A is 0101001. Numbers however can take several forms.