A subset is a portion of the data in the worksheet. Some Minitab functions, including many graphs and charts, let you define a subset of data in order to work with it in isolation without changing the data in the worksheet itself. For example, your worksheet may contain data for the entire year, but you want to create a time series plot of only the previous six months. Using the subset option lets you graph only those data points that came after your specified date.
When you create a graph, you can specify a subset of data to graph.
You have the following data in a worksheet and you would like to create a time series plot that includes only the data from 1/2/2014 to 1/7/2014 on the time series plot.