JDL (http://www.jhipster.tech/jdl/) is used to create the domain model for a JHipster application. It provides a simple and user-friendly DSL to describe the entities and their relationships (for SQL databases only).
JDL is the recommended way to create entities for an application and can replace the entity generator provided by JHipster, which can be difficult to use when creating a lot of entities. The JDL is normally written in one or more files with a .jh extension.
Visit http://www.jhipster.tech/jdl/ for complete documentation on JDL.
If you prefer to work with UML and UML modeling tools, then check out JHipster-UML (http://www.jhipster.tech/jhipster-uml/), a tool that can create entities from popular UML tools.
