A Directed Acyclic Graph (DAG) is a type of data structure that consists of nodes and edges, where each edge has a direction and there are no cycles. This means that you cannot start at one node and follow the edges to return to the same node. DAGs are useful for representing relationships where order matters, such as in scheduling tasks or organizing dependencies. In computer science, DAGs are often used in various applications, including version control systems like Git, where they help track changes in files. They are also employed in blockchain technology to improve scalability and efficiency, allowing multiple transactions to be processed simultaneously without conflicts.