Spring Boot is an open source framework for building microservices and web applications. It is based on Spring and includes additional features such as embedded Tomcat and undertow servers so applications can be started using java -jar. Spring Boot aims to simplify configuration and provide production-ready features so developers can focus on writing business logic rather than boilerplate configuration code. It has gained popularity since its release in 2014 with over 800,000 downloads and a large developer community on GitHub.