Spring is an open source integration framework for Java applications. It began in 2002 as an alternative to EJB and has since expanded into a full application development framework. It provides core features like inversion of control (IoC) and dependency injection (DI) and supports various web frameworks, data access technologies, messaging, and cloud technologies. The Spring community has grown significantly in recent years, with over 15 million projects generated from start.spring.io in 2019 alone.