What are lo-fi and high-fi designs?
Lo-fi / hi-fi stands for low / high fidelity, the degree of exactness with the intended final design. As product teams work with different features to potentially build, they can be much more effective is they learn to work with increasing degrees of fidelity. As a feature becomes progressively more validated and refined, the team can invest more in the design and move from sketch, to wireframe, to mockup, to prototype, and to final design (sometimes skipping a step or two).
Lo-fi / high-fi designs are part of refinement step of collaborating to figure out how to build a feature, a part of the product management process.