Sax is a streaming XML parser for Node.js, designed for speed and efficiency. Unlike DOM-based parsers, Sax doesn't load the entire document into memory, making it suitable for large XML files. It reports events as it encounters them, such as opening and closing tags, attributes, and text content, allowing for real-time processing. Sax is highly configurable, supporting various XML features and encodings, making it a flexible choice for diverse XML parsing needs. This makes it a popular choice for efficient data extraction and transformation.