You can put this solution on YOUR website! There are a couple of definitions of linear in mathematics, but I suspect you are looking for the following:
A polynomial of degree 1 is said to be linear, because the graph of a function of that form is a straight line.
Over the reals, a linear function is one of the form:
m is often called the slope or gradient; b the y-intercept, which gives the point of intersection between the graph of the function and the y-axis.
