Big Hairy Audacious Goal (BHAG)

A clear and compelling 10-to-30-year goal that serves as unifying focal point of effort, and acts as a clear catalyst for team spirit. It has a clear finish line, so the organization can know when it has achieved the goal; people like to shoot for finish lines.
From James Collins' and Jerry Porras' 1996 article entitled "Building Your Company's Vision."