PouchDB is an open-source JavaScript database that is designed to run within web browsers. It enables developers to build applications that work offline by replicating data from a cloud database down to the local device. This functionality allows users to access and interact with their data even without an internet connection. PouchDB is modeled after the CouchDB database and can sync seamlessly with CouchDB and compatible servers. Offering cross-browser support and a straightforward API, PouchDB is a popular choice for developers looking to create resilient, offline-first web and mobile applications.