A line of best fit is a straight line that is the best approximation of the given set of data. In simple term, it is a graphical representation.
A more accurate way of finding the line of best fit is the least square method. If you draw a line of best fit, it is possible to determine the equation of the line of best fit. You will remember that the equation of a straight line is given by
m is the gradient
c is the intercept
Example: The points with coordinates (0, 6), (2, 7), (4, 8) and (6, 9) lie on a straight line. Draw the line and determine its equation.
The following graph shows a scatter plot and a line of best fit: