Spring is a great web framework and one of the most popular ones in the Java world. With Spring Boot it became even better. Spring Boot prefers convention over configuration and that eliminates a lot of boilerplate code. It's easier to write configurations. As a result, it feels more lightweight, unlike Spring Framework. Spring Boot is a microservice ready platform.
In a nutshell, Spring Boot helps you to quickly bootstrap your product, and it includes helpful features to push your application to production with almost no fuss.