1Y Max Loss Indicates the maximum fall in the value of the investment over the previous 1 year; In simple terms, it is the % return an investor would have made if they would have bought a stock at the highest price point and sold and the lowest price point in the past year. It gives investors an idea of the worst-case return if they decide to invest in a particular stock. 

Also known as maximum drawdown, the calculation of this metric is not as straightforward as the % difference between the 52 week high and low. Since the low could be before the high, that might not necessarily be your worst return, rather the % difference between 52 week high and the lowest point occurring after it would be your max loss.