Maven is a build tool that manages Java projects and automates tasks like compiling code, running tests, generating reports and managing dependencies. It uses a Project Object Model (POM) file to store build configuration and metadata. Maven projects can contain parent and child subprojects, each with their own POM. It builds projects in a defined order and generates artifacts like JARs and WARs that can be deployed. Maven plugins are used to perform tasks like compiling, testing, packaging and deploying the project.