(grammar) A type of plural-only noun denoting an object which consists of two parts joined together, e.g., scissors, pants, eyeglasses.

(algebra) Any operation taking two operands.

(computing) A number represented by the binary digits 0 and 1.

(computing) Either of the characters 0 and 1, used in the binary numeral system.

(computing) A code that uses the binary digits (1 and 0), usually in groups of eight, to represent characters, machine instructions or other data.

(mathematics, computer science) A data structure in which each node has at most two children, each node but the root has one parent, and there are no cycles.

(chemistry) A chemical compound composed of only two elements. / (chemistry) A compound composed of an element and a radical (a group of atoms that behave as one piece).

(arithmetic) arithmetic using binary numbers

(astronomy) A stellar system in which two stars orbit around their center of mass; double star.

(set theory, order theory, "on" a set A) A subset of the Cartesian product A×A (the set of ordered pairs (a, b) of elements of A).