As I work with businesses and organizations, this word is definitely thrown around, a lot. But I don't think a majority of high level leaders truly grasp it's meaning, beyond the trendiness of saying it like you mean it.
What it is not.
It's not acting like you care, or are vulnerable, when in fact your ego is still driving 97% of the time. It's not once and a while having a token meeting with team members to let them speak their minds, only to patronize them with little information back, and little implementation of their ideas. It's not dripping superficial news to your team, then acting like you've just "dropped the waterline."
What it is.
It varies, from one person or company to the next. But it's taking a deeper look at your organization and team, honestly. It's admitting the things that need improvement, and not making light of mistakes, including yours as a leader. In fact, it's mostly being transparent with oneself. You see, when we are ready to be relentlessly honest about where we are, what's not working, what are our shadow sides... we are ready to look at our businesses in the same "no excuses" way.
This humble, honest approach leads us to more victory, less pride and pomp, and more approachability from others.