DAG stands for Directed Acylic Graph and is graph-theory. Practical applications of the theory are source code or document version management (git), genealogy, data compression (xml compression) and distributed ledgers like [[obyte]].

https://en.wikipedia.org/wiki/Directed_acyclic_graph

https://www.youtube.com/watch?v=5hg8Ahp3d58

https://kbaiiitmk.medium.com/directed-acyclic-graph-dag-based-distributed-ledgers-e2f42c39366

https://www.researchgate.net/publication/349180278_Directed_Acyclic_Graph_Based_Blockchain_Systems