The Web Audio API is a powerful browser API for creating, manipulating and analyzing audio. The application uses React to create a user interface that allows users to access their microphone and visualize the audio data on a canvas. The audio analysis is performed using the Web Audio API's AnalyserNode, which breaks down the audio signal into frequency bins and provides a visual representation of the sound wave. The visualization is updated in real-time as new audio data is received from the microphone. The application demonstrates how to access the microphone, setup the Web Audio API, analyze audio, and visualize it on a canvas using React.