Imagine you have two internet lines coming into your business. Each internet line would come into your business and be hooked straight to a routing system. From the routing system the internet connection is propagated to various devices in the business.
Internet lines do on occasion fail. If one of the lines were to fail, then half of your business complex would not have an internet connection. Workers in half your complex would be non productive towards business matters.
This is how to keep your workers productive watching their entertaining youtube videos while at work. How? Imagine if you could have a set of routing systems communicating with each other. The routing systems would provide redundancy to each other. Therefore allowing for internet connection to remain active across your entire business.
However in the event that both your internet connections were to go down at the same time. Then redundancy would have failed. Bringing up productivity to more work related matters. Your internal network would still be able to allow communication between machines. There just would not me any internet for research and entertainment.
So there you have it. That is a Mesh network. Just don't tell your boss about it, or you'll have to do work.