Precalculus (6th Edition) Blitzer

Inequality symbols like $,\le,\ge$ are used to express the inequality between $x$ and $y$.
A system of linear inequalities in two variables $x$ and $y$ are the equations which will use the various inequality symbols like $,\le,\ge$ to represent the relation between $x$ and $y$. In the linear inequality, the power of variables $x$ and $y$ is always one. Some examples of linear inequalities are shown below: \begin{align} & 3x-6y\ge 20 \\ & x+2y\le 5 \\ & x<0 \\ \end{align} Hence, the inequality symbols $,\le,\ge$ are used to express linear inequalities in two variables $x$ and $y$.