The slope of a straight line is the tangent of the angle that the line makes with the positive x-axis. As the tangent of an angle in a right triangle is the opposite side/adjacent side it is equal to the change in the y value for a unit change in the x value.
The slope of a straight line is simply the "rise" over the "run." In other words, the slope of the line tells us how many units the line goes up for every unit that it goes horizontally. The slope of a line can be positive (the line rises as it goes to the right) or negative (the line goes down as it goes to the right).
The meaning of a slope of a straight line is the changes of y value when the x value changes.
The slope is usually written as m.
m = (y2-y1)/(x2-x1)
So, the slope shows the rate at which the value of y changes with respect to the value of x.
For instance, m=5/4 means that The value of y will increase by 5 units for every 4 units of x.