An Elevator Speech is a super-short explanation of an idea, a business, or a blog, designed to create further interest that can be delivered in the time it takes folks to ride from the top to the bottom of a building in an elevator.
These days bloggers and business people are delivering their elevator speeches ie. the by using the 140 character capability of the twitter platform.
Here is an elevator speech worth watching: Twitter in Plain English
Creating a 140 character twitter elevator speech is a challenge. Why not try it? You may find you learn something by the exercise.