An adjusted close is a historical closing price recalculated for dividends, stock splits, and other corporate actions. It provides a more consistent price series for estimating historical returns. section 3.1.1
From prices to returns
Download the Adj Close column for AAPL, FE, and WMT, then compute daily returns with pct_change(). Annualize the mean daily return by multiplying by approximately 252 trading days. The first return is NaN because no prior price exists. section 3.1.1
Adjusted prices are appropriate for historical-return analysis, but not every simulation. A dividend-receiving portfolio backtester should use Close prices and model dividends as separate cash income rather than using Adjusted Close. section 13.4.2
