Directed Acyclic Graph (DAG) refers to a data structure that is built in one single direction, yet branches out and never repeats.
Directed = Connections between two points (nodes) have directions such that A -> B is not the same as B -> A.
Acyclic = Opposite of cyclic where you’ll end up where you started from after some time. In an acyclic system, you’ll never encounter the same point (node) twice.
Graphs = A structure consisting of points (nodes) that are connected.
Compared to a regular blockchain data structure which operates in one straight chain, DAG based systems have more breadth as the network is similar to a expanding tree rather than a straight chain.
Yes, and this is an alternative of blockchain. Some crypto's use it, but I have not understood the propagation, to the network, to avoid double spending.