Short answer: Spring Boot is an opinionated layer on top of the Spring Framework that removes setup work, so you can run a production-ready application with very little configuration.
What Spring Boot adds:
- Auto-configuration: it looks at the libraries on the classpath and configures beans for you (for example, a DataSource when a JDBC driver and spring-boot-starter-data-jpa are present).
- Starters: curated dependency sets such as spring-boot-starter-web that pull in compatible versions together.
- Embedded server: Tomcat, Jetty or Undertow runs inside the app, so you ship one executable JAR instead of deploying a WAR to an external server.
- Production features: Actuator for health checks and metrics, externalised configuration through application.yml, profiles and environment variables.
What stays the same: dependency injection, AOP, transactions and Spring MVC are still the Spring Framework. Spring Boot does not replace them; it wires them together with sensible defaults that you can override.
When to say this in an interview: emphasise that Boot trades a little flexibility for speed and consistency, and that every default can be replaced by defining your own bean or property.