Defining a Linear Equation. This lesson is on what a linear equation is. And the answer to that question is essentially a linear equation is any pattern of numbers that is increasing or decreasing by the same amount every step of the way. This means that the only two things that we need to define a linear equation are where the pattern begins and what that pattern moves by. What that leaves us with is the slope-intercept form of the linear equation, y = mx + b, where the m value is the slope, and the b value is the y-intercept.