In Lean Startup an experiment is a product with paying customers

In the Lean Startup model, an experiment is more than just a theoretical inquiry; it is also a first product. If this or any other experiment is successful, it allows the manager to get started with his or her campaign: enlisting early adopters, adding employees to each further experiment or iteration, and eventually starting to build a product. By the time that product is ready to be distributed widely, it will already have established customers. It will have solved real problems and offer detailed specifications for what needs to be built. Unlike a traditional strategic planning or market research process, this specification will be rooted in feedback on what is working today rather than in anticipation of what might work tomorrow.

Questions to ask;

1. Do consumers recognize that they have the problem you are trying to solve? 
2. If there was a solution, would they buy it? 
3. Would they buy it from us? 
4. Can we build a solution for that problem?”

“Success is not delivering a feature; success is learning how to solve the customer’s problem.”

The Lean Startup: How Today's Entrepreneurs Use Continuous Innovation to Create Radically Successful Businesses by Eric Ries