This shows stocks that are trading at their highest price over the last 52 weeks (12 months). Academic research suggests that stocks at or close to their 52 week highs tend to outperform.
This is apparently because investors use the 52- week high as an "anchor" against which they value stocks, thus they tend to be reluctant to buy a stock as it nears this point regardless of new positive information. As a result, investors underreact when stock prices approach the 52-week high, and consequently, contrary to most investors' expectations, stocks near their 52-week highs tend to be systematically undervalued.
You can read more about 52 week highs here.