Here's a great video explaining airbnb's big idea and what their logo represents:
And I like how they articulate their mission on their blog:
We asked ourselves, “What is our mission? What is the big idea that truly defines Airbnb?” It turns out the answer was right in front of us. For so long, people thought Airbnb was about renting houses. But really, we’re about home. You see, a house is just a space, but a home is where you belong. And what makes this global community so special is that for the very first time, you can belong anywhere. That is the idea at the core of our company: belonging.