display_errors determines whether errors should be printed to the screen as part of the output or if they should be hidden from the user. By default this is turned off, but could be a very useful tool if you're troubleshooting why a site isn't loading correctly.
To turn this on, first log in to the Platform and select the website from the dashboard and then select either Upgrade PHP Version or PHP & Databases from the site menu.
Scroll down to the PHP Configuration section and click Add Variable. Type display_errors in the first box and select either on or off in the Value box. Click Update Configuration to save the changes.