A best fit line is a straight line that represents the trend of a set of data points. It is used to predict the value of a dependent variable based on the value of an independent variable. In Excel, you can create a best fit line by using the Chart Tools menu.
Best fit lines are important because they can help you to identify trends in data and make predictions. For example, if you have data on the sales of a product over time, you can create a best fit line to predict future sales.