Simple Moving Average
Simple moving average is the most common among the moving averages. It is computed by taking the mean or average of prices over a given period. Prices can be the daily open, high, low, close (most widely used), volume, et cetera of a given security.
The 9-day moving average is calculated by averaging the first nine days. On Day 10, the prices of Day 2 through Day 10 are added and divided the total by 9 and so on.
Just always remember that a moving average with a shorter period has a greater probability of receiving false signals as compared to a longer moving average which has less sensitivity to recent changes in the data.