The Money Flow Index is a volume-weighted Relative Strength Index. It uses price and volume to measure trends in buying and selling.
The conventional Relative Strength Index (RSI) compares the magnitude of a stock’s recent ‘up closes’ (where the price closed higher than it opened) to recent ‘down closes’ (where the price closed lower than it opened). The results are then indexed from 0 to 100.
The difference with the MFI, is that instead of using close prices, it uses the typical price multiplied by volume.