A moving average smooths price data by calculating the average price over a rolling window. The two most common are the Simple Moving Average (SMA) and Exponential Moving Average (EMA).
SMA(n) = Sum of last n closing prices / n
The 50-day SMA is the average of the last 50 closing prices. When a stock's price crosses above its 200-day SMA, it's often interpreted as a bullish signal (a "golden cross").
AllInvestView displays moving averages on stock price charts with customisable periods.