What is the difference between AI, ML, NN and DL?
AI: a super general term, means a bit of everything... and nothing at the same time. It's all about building intelligent machines, even though its meaning is not fully developed. It's not used in a rigorous way at all. In fact, scientists prefer to use more technical terms like the others you listed.

ML: it's an approach to data, and it's all based on building models that improve automatically from experience.

DL: Deep Learning, it's the subset of ML that makes use of Deep Neural Networks. So technically it's still Machine Learning, currently its most advanced and promising branch.

NN: The general class of models that is employed in DL. DL is the field of application of NN's.


Personally, I don't really like that Venn diagram you posted. DL being a subset of NN... that doesn't make sense to me.