A Moving Average is a widely used indicator in technical analysis that helps smooth out price action by filtering out the “noise” from random price fluctuations.
A moving average (MA) is a trend-following or lagging indicator because it is based on past prices.
The two basic and commonly used MAs are the simple moving average (SMA), which is the simple average of a security over a defined number of time periods, and the exponential moving average (EMA), which gives bigger weight to more recent prices.
The most common applications of MAs are to identify the trend direction and to determine support and resistance levels. Investopedia
Below When the price moves above the 21 day moving average we are ready to trade, and when the price fully moves below the 21 day ma then we are ready to sell.