Directed acyclic graph
Directed acyclic graph (DAG) is a directed graph with no directed cycles, but may have “parallel” paths that go from one node and arrive at the end node by different paths.
In other words, it is a graph in which the edges go in one direction, but there are no loops — it is impossible to reach the origin or the same node.
DAG is often considered as a competitor to blockchain or as the next generation of blockchain. But in reality they are more like “relatives” and at the same time competitors. Both are distributed ledgers, but blockchain is a linear distributed ledger, and a directed acyclic graph has no chain of blocks, ledgers without a blockchain.