So sad that you have to ask. It's a mandate, not a buzzword. If you need someone in authority or a rule book to TELL you  what it means, that's sad too. Maybe my mother said it best, and often "Use the brain God gave you." 

The rejection or cavalier use of that gift in the name of compliance, obedience, subservience, lesser status, rules, directives,  and uniformity allows one to opt out of  hard work, sacrifice, diligence, rigor, and responsibility of God's demand of us to use the brain (and viscera, and experience, and education, and expertise) He gave us adults to discern. 

To discern is to risk "to learn." And as John Wooden said, learning can happen only after you know it all.