"Gospel humility" is the humble attitude that results when an individual personally encounters Jesus Christ and the reality of the Gospel: the good news that Jesus came, suffered, and died a horrible death for our sins so that we could be reconciled to God, as a free gift to undeserving sinners.
The thing about Gospel humility, however, is that the more you talk about it the more it becomes an idea, a concept, or a "religious goal," rather than a symptom of my personal realization that I am just as much as part of the sinful, broken mess that Jesus came to redeem as anyone else. Tim Keller, in an article in Christianity Today, wrote, “Humility is so shy. If you begin talking about it, it leaves” (Dec. 2008, p. 51). So true.
It is a symptom, like a runny nose to someone who is infected with a cold virus; or, using a more positive image, it is like warmth on you skin after you have sat in front of a cozy fireplace for an evening. It is like the wetness of water or the brightness of light. You can't cultivate it by reading about it or talking about it. You don't get it by becoming an armchair theologian and knowing all the answers. It comes as you walk through life and, with each fallen step, become increasingly stunned by the sorrow of your own failures and unbelief and hardness and selfishness, how you have deeply failed people you love, and how you have therefore failed all the more the One who loves you most, combined with the reality of the bleeding, broken Lamb who whispers into the pain of you inner world, "This is why I came."