Definition:Common Divisor

Integral Domain
Let $\left({D, +, \times}\right)$ be an integral domain.

Let $S \subseteq D$ be a finite subset of $D$.

Let $c \in D$ such that $c$ divides all the elements of $S$, that is:


 * $\forall x \in S: c \backslash x$

Then $c$ is a common divisor (or common factor) of all the elements in $S$.

Integers
The definition is usually applied when the integral domain in question is the set of integers $\Z$, thus:

Let $S$ be a finite set of integers, that is:


 * $S = \left\{{x_1, x_2, \ldots, x_n: \forall k \in \N^*_n: x_k \in \Z}\right\}$

Let $c \in \Z$ such that $c$ divides all the elements of $S$, that is:


 * $\forall x \in S: c \backslash x$

Then $c$ is a common divisor (or common factor) of all the elements in $S$.