Definition:Binary Notation

Definition
Binary numbers are numbers expressed in base $2$ notation.

That is, every number $x \in \R$ is expressed in the form:
 * $\displaystyle x = \sum_{j \mathop \in \Z} r_j 2^j$

where $\forall j \in \Z: r_j \in \left\{{0, 1}\right\}$.

Also see
Binary numbers, like hexadecimal numbers, have particular relevance in the field of computer science.