jQuery is a fast, small, and feature-rich JavaScript library designed to simplify client-side scripting of HTML. Its famous motto, "write less, do more," encapsulates its core purpose: to make tasks like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers. By abstracting away cross-browser inconsistencies, jQuery played a foundational role in the evolution of modern web development, and while many of its concepts are now integrated into native JavaScript and modern frameworks, it remains a widely used and influential library in countless existing web applications.