PhoneGap is a framework that allows developers to build mobile apps using HTML, CSS, and JavaScript instead of platform-specific languages. It provides an API to access common device capabilities like contacts, location, and cameras. PhoneGap works by wrapping web-based apps in a native container, so they can be compiled and run as native apps on iOS, Android, and other platforms from a single codebase. This allows developers to write their app once and deploy it across platforms, rather than maintaining separate codebases for each one.