A diagram that outlines the full experience of the customer - online, offline, the opportunities, the challenges and problems.
Like personas, they're a catalyst rather than an end result. Something to inspire and steer a group of stakeholders.
Adaptive Path's user experience map for Rail Europe
The Anatomy of an Experience Map - article by Chris Risdon for Adaptive Path
PDF download of the Rail Europe experience map from Adaptive Path
Experience Maps: Understanding Cross-Channel Experiences For Gamers - article and examples by Gene Smith