p5.js is a JavaScript library that makes it easy to create interactive, graphical applications, including games, simulations, and visualizations. It offers a wide range of features and tools, including support for graphics, animation, and user input, as well as a range of built-in functions and classes for tasks such as image processing and sound generation. p5.js is widely used by artists, designers, and educators, and it is particularly popular in the fields of data visualization and generative art.