Fidelity has to do with how realistic the prototype looks. A low or even medium-fidelity user prototype doesn’t look real – it is essentially an interactive wireframe. “User prototype” means that it is a simulation and not something real. In other words, you can enter your credit card info as many times as you want, you won’t actually buy anything.

Balasamiq is pretty much everyone’s favorite low-fidelity user prototyping tool as they have made it so quick and easy to create this form of prototype. Low–fidelity user prototypes are typically created by the interaction designers. Many teams use these as a way to think through the product among themselves. For certain situations you can also identify usability issues right at this very early stage.

As great as they are, low-fidelity user prototypes only represent one dimension of your product – the information and the workflow – there’s nothing there about the impact of visual design, or the differences caused by the actual data, as just a couple important examples.