A directed acyclic graph is a directed graph that contains no cycles. In Gradle each task to execute represents a node in the graph. A dependsOn relation to another task will add this other task as a node (if it is not in the graph already) and create a directed edge between those two nodes. Any dependsOn relation will be validated for cycles. There must be no way to start at certain node, follow a sequence of edges and end up at the original node.
A domain-specific language is a programming language or specification language dedicated to a particular problem domain, a particular problem representation technique, and/or a particular solution technique. The concept isn't new—special-purpose programming languages and all kinds of modeling/specification languages have always existed, but the term has become more popular due to the rise of domain-specific modeling.