Flat design is a minimalist design approach that focuses on simplicity and clarity. It eliminates embellishments like shadows, textures, and gradients, opting for clean lines and solid colors instead. This design style became popular as a response to the skeuomorphic design trend, which tried to mimic real-world objects in digital interfaces. Flat design is highly functional, making it easier for users to understand what each element does.

However, this doesn't mean flat design is purely aesthetic; it aims to enhance usability by making interface elements easy to recognize. While it has its pros, like faster load times and easy adaptability across devices, it can sometimes lack the cues that tell users how to interact with elements. So, good flat design often incorporates some level of depth or cues to guide user interaction.