An equation in two variables that graphs as a straight line is called a linear equation because it:

1. The name describes the shape of the graph. 2. Equations with two variables may be of a standard form. 3. Equations of this form are called linear equations in two variables. 4. The word linear points to the shape they produce. 5. So the name comes from graphing as a line. _Source: OpenStax Elementary Algebra 2e (CC BY 4.0), Ch 4 'Graphs', sections 4.1-4.7_