In mathematics, a (sometimes called just domain) an integral domain R with the property that any two elements have a greatest common divisor; i.e., there is a unique minimal principal ideal containing the ideal generated by two given elements.

The binary GCD algorithm, also known as Stein's algorithm or the binary Euclidean algorithm, is an algorithm that computes the greatest common divisor of two nonnegative integers.

Lehmer's GCD algorithm, named after Derrick Henry Lehmer, is a fast GCD algorithm, an improvement on the simpler but slower Euclidean algorithm.