The PE Buy/Sell Zone on a stock overview page shows whether a stock is trading in the Buy or Sell Zone based on its historical price-to-earnings ratio (PE ratio). 

The PE ratio compares a company's stock price to its earnings per share, determining whether it is overvalued or undervalued. This section also shows the percentage of time the stock has traded below its current PE level.

For example, Infosys is in the Sell Zone in the screenshot below, as its P/E when checked was historically lower than the current P/E value.