From here.

A Merkle DAG is a Merkle directed acyclic graph. That is a data structure similar to a Merkle tree but not so strict: such DAG does not need to be balanced and its non-leaf nodes are allowed to contain data.

It seems the projects “Bitcoin”, “git” and “ipfs” all have the “Merkle tree” concept in their implementation. Interesting…

Here is a Merkle tree example: