Minimum Viable Product is essentially a working, commercialised prototype of the grand future end product, which has just enough features to satisfy early customers, while also including mechanism for getting feedback and suggestions which may potentially be incorporated into the future designs. This is useful especially to avoid wastage or expenses in adding non necessary features in initial design, instead letting the customer decide the features that may prove useful in the later design stages that could be potentially more profitable.
Examples:
1. AirBnB : Started with an air inflatable mattress in living room with breakfast included. Advertised on Craigslist by the founders to make some extra pocket money. This expanded to other house owners and now is one of the modern age success stories.
2. Amazon : Started as an online book catalogue where jeff Bezos would take an order, buy from the distributor and ship it to the buyer. This then expanded to include CDs, computer parts, software, music etc..all from his garage. The rest is history.
3. In general, most crowdfunded products online are MVPs, the best example being the iconic Pebble Smartwatch which started with a basic premise, garnered feedback for its further iterations and for the relatively brief time it lasted, blazed a trail of glory in the Smartwatch industry and inspired other smartwatches.
Note: To be an MVP, it should be commercially viable, meaning it should generate income even as an early 1st iteration or prototype.