A line of best fit, also known as a regression line, is a line of fit that estimates the relationship between the values of a data set. The equation of the line of best fit has been determined using a strict mathematical method.

One commonly used method to determine a line of best fit is the method of least squares. The methods used to find the line of best fit are usually hard to do by hand. Therefore, a line of best fit can be found by performing a linear regression on a graphing calculator. As an example, consider the data set graphed above.

x	y
0.6	1.5
1.2	3.6
2.6	5.2
3.6	6.3
4.5	8.7
6	10.3
6.6	11.8
7.1	11.7

In reference to the graph, the data points appear to closely follow the line y = 1.55x + 1.14. Consequently, even if the data points may not precisely align with any specific line, a linear model can be considered to adequately describe the data.