Spring MVC is a sub-project of the Spring Framework, targeting design and development of applications that use the MVC (Model-View-Controller) pattern. Spring MVC is designed to integrate fully and completely with the Spring Framework and transitively, most other sub-projects.
Spring Boot can be understood quite well from this article by the Spring Engineering team. It is supposedly opinionated, i.e. it heavily advocates a certain style of rapid development, but it is designed well enough to accommodate exceptions to the rule, if you will. In short, it is a convention over configuration methodology that is willing to understand your need to break convention when warranted.
