The mean is the average response for each combination of control factor levels in a static Taguchi design. Depending on the response, your goal is to determine factor levels that either minimize or maximize the mean.
For example, you want to know how four control factors affect the flight distance of golf balls. The means for this example provide an estimate of flight distance at each factor level. Because you are interested in maximizing flight distance, you want to determine factor levels that result in the largest means.