\begin{definition}[Definition:Coordinate System/Coordinate]
Let $\sequence {a_n}$ be a coordinate system of a unitary $R$-module $G$.
Let $\ds x \in G: x = \sum_{k \mathop = 1}^n \lambda_k a_k$.
The scalars $\lambda_1, \lambda_2, \ldots, \lambda_n$ can be referred to as the '''coordinates of $x$ relative to $\sequence {a_n}$'''.
\end{definition}