uuid is a JavaScript library for generating RFC4122 compliant UUIDs (Universally Unique Identifiers) in various versions (v1, v3, v4, v5) and formats. It's widely used for creating unique identifiers in applications, databases, and distributed systems. The library is lightweight, has no dependencies, and supports different environments including browsers and Node.js. It ensures uniqueness and allows for generating UUIDs based on different data sources and hashing algorithms.