The Business Model Canvas is a visual tool that allows you see to your entire business model on one page. It is supposed to be continually updated as your business progresses.
The Business Model Canvas was designed by Alexander Osterwalder, as part of his PhD from HEC Lausanne.
The categories in the Canvas are: customer segments, value proposition, customer relationship, channels, key activities, key resources, key partners, cost structure, and revenue streams.
If you work in a team, then the Business Model Canvas works best when printed out on a large surface. That way groups of people can add to the Canvas. Usually, people use sticky notes.
An easy read for further reference is the Business Model Generation by Alexander Osterwalder and Yves Pigneur.
Also, more detail can be found on Wikipedia: http://en.wikipedia.org/wiki/Business_Model_Canvas