Answer
Yes, all linear equations in two variables in the form $y=mx+b$ where $m\ne0$ define functions.
$\\$ Please refer to the step by step part for the explanation.
Work Step by Step
The graphs of linear equations of the form $y=mx+b$ where $m\ne0$ are diagonal lines.
$\\\\$When the vertical line test is performed, all vertical lines will pass through at most one point on the graph of linear equations in two variables.
$\\\\$Therefore, all linear equations in two variables define functions.