The process of showing design mockups to prospects, users, or potential users to get feedback on design plans and overall direction from people that would actually use the product.
Here's an analogy.
Imagine being able to test drive your kitchen redesign before you committed to it. You’d get to see whether you can reach all the cabinets and if the placement of the appliances fits the way you like to cook. You learn more from testing it out than you do from looking at pictures.
Why does it matter?
User validation lets you test whether your hypothesized design and workflow improvements work for your key personas, so you can make any revisions before they become costly and time-consuming for your business.
How does it apply?
Before releasing the product or beginning development, the user validation step gives you additional confidence that the solution of your digital product is the right one for your target users. The process also helps eliminate unnecessary work for the development team.