A rational number is one which can be written as \(\dfrac{m}{n}\) where \(m\) and \(n\) are integers with \(n\ne0\). That is, it can be written as a ratio, hence the name.
For example, \(-17\), \(\frac{2}{5}\) and \(-\frac{1013}{12}\) are rational, but none of \(\pi\), \(e\) or \(\sqrt{2}\) is.
We use the symbol \(\mathbb{Q}\) for the set of rational numbers.
