Maven comes with three standard lifecycles: default, clean, and site. Each lifecycle defines its own set of phases.
The clean lifecycle defines three phases: pre-clean, clean, and post-clean. A phase in a lifecycle is just an ordered placeholder in the build execution path. For example, the clean phase in the clean lifecycle cannot do anything on its own. In the Maven architecture, it has two key elements: nouns and verbs. Both nouns and verbs, which are related to a given project, are defined in the POM file. The name of the project, the name of the parent project, the dependencies, and the type of the packaging are nouns. Plugins bring verbs into the Maven build system, and they define what needs to be done during the build execution via its goals. A plugin is a group of goals. Each goal of a plugin can be executed on its own or can be registered as part of a phase in a Maven build lifecycle.
When you type mvn clean, it executes all the phases...