...
Return represents the total return of a security: the current market value, plus the income taken out as cash, plus cash received from sales of shares, minus the amount invested.
Reinvestments are not explicitly added to the return, because they contribute to the market value, which is already factored in.
Note that Return (%) YTD is based on downloaded data and is not affected by changes in the As of date option.
Let's say you bought 100 shares for $5 each ($500 total). You later sold 50 shares for $6 each ($300 total). Now the market price of your 50 remaining shares is $7 ($350 total).
The return is $350 (current market value), plus $300 (sales), minus the $500 you invested, for a total return of $150.