What is the meaning of Quaternion?

A group or set of four people or things.

A word of four syllables.

A type of four-dimensional hypercomplex number consisting of a real part and three imaginary parts (real multiples of distinct, independent square roots of −1 denoted by i, j and k); commonly used in vector mathematics and as an alternative to matrix algebra in calculating the rotation of three-dimensional objects.

quaternion

Source: wiktionary.org