pnpm, which stands for "performant npm," is a fast and disk space-efficient package manager for the Node.js ecosystem, serving as a powerful alternative to npm and Yarn. Unlike traditional package managers that duplicate dependencies for each project, pnpm utilizes a content-addressable store on the disk to store a single instance of each package version. It then uses hard links and symlinks to connect these shared packages into a project's `node_modules` directory, resulting in significantly faster installation times and massive disk space savings. This unique linking strategy also creates a strict, non-flat `node_modules` structure, which enhances project reliability by preventing unauthorized access to undeclared or "phantom" dependencies.