What are linear equations in one variable?

Linear equations in one variable :

• A linear equation is an equation of a straight line. 
• The power of the variables should be 1. Linear equations in one variable may take the form $ax + b = c$ and are solved using basic algebraic operations.

For example,

$2x+3=8$ is a linear equation having a single variable in it.

The highest power of the variable is 1 means the power of the variable should be 1, it cannot be 0 or more than 1.