Microsoft SharePoint team has released an excellent video that explains in simple terms what SharePoint is, and why/how people use it.
If you’re dealing with people who are new to SharePoint and finding it hard to explain what it is, this video might be a savior. It also great to include in a client pitch where at times most of the business folks have no clue about SharePoint.
The video is slow. Usually when you run it for first time, it takes time but for subsequent time it should run without getting information from net instead it should catch it from catche. I tend to loose interest when it pauses for gathering information from net after every 1 min gap