The Chaikin money flow indicator was created by Marc Chaikin to calculate the amount of money that is flowing into or out of a currency or security. The main purpose for Chaikin creating the Money flow (CMF) was so he had an oscillating indicator to use with his previous cumulative indicator, Accumulation and Distribution. The calculations are generally over a 20 or 21 day period with the indicator often fluctuating above or below the zero line in the same way an oscillator fluctuates.
From this point, many chartists look at the pressure of buying or selling and weigh that against the absolute level of the CMF. To identify changes in money flow, they will also look out for any crosses above or below the zero line.