Maven is a build tool that manages Java projects and their dependencies. It uses a POM (Project Object Model) file to describe build configuration including dependencies, plugins, and reports. The document discusses using Maven to build a sample Java project with modules including data, EJB, and web application components. Maven allows each component to be built independently and deployed as JAR, EJB-JAR, and WAR artifacts. XDoclet and other plugins are used to generate code and handle deployment details.