What does it mean if I see "security recommendation" next to a wifi network?
It's new with iOS 10.  Here's an overview of the feature by Engadget:


  After connecting to an open network, iOS 10 will display a "Security Recommendation" notification beneath the network's name in the WiFi menu settings. When a user opens up the Security Recommendation, they're greeted with a notification that "open networks provide no security and expose all network traffic." There's also a recommendation to configure your router to use AES encryption for the network.