Chart.js is a popular open-source JavaScript library that allows developers to create simple yet flexible charts and graphs for web applications. Designed for use with HTML5 canvas elements, it provides easy-to-use rendering tools to produce interactive and responsive chart types such as line, bar, radar, doughnut, and pie charts, among others. Chart.js is highly customizable and lightweight, making it an excellent option for developers looking to add data visualization capabilities to their projects without significant overhead.