The document discusses implementing domain specific languages (DSLs) using Groovy. It defines DSLs as languages that clearly express the ideas of a particular domain. It outlines several advantages of Groovy for building DSLs, including its flexibility, Java interoperability, and features that support DSL development like introspection, syntactic sugar, and operator overloading. Examples are provided of internal DSLs implemented in Groovy for tasks like querying a database and defining recipes.