DAG is short for "Directed Acyclic Graph". It's another way of c

Nowadays there are IOTa, RaiBlocks and Bytesball that use DAG instead of Blockchain.
You can read about it here:
https://getacryp.com/blockchain-vs-tangle-dag/
This one describes the technology in quite a simple language.

Here is some more info
https://bitcointalk.org/index.php?topic=1799665.0
https://en.wikipedia.org/wiki/Directed_acyclic_graph
http://ericsink.com/vcbe/html/directed_acyclic_graphs.html

Segreto believes that DAG is more suitable for Messenger than blockchain (regarding message storing).

Yours,
ς.