Lunr.js is a lightweight, full-text search library for use in browsers and Node.js. It enables fast and relevant search functionality directly within your application, eliminating server-side dependencies for simple search needs. Lunr.js indexes your data client-side, allowing users to quickly locate information without constant server requests. It supports stemming, stop word filtering, and field boosting for refined search results, and its small size minimizes impact on page load times.