Deep Learning is a subset of Machine Learning algorithms.
It typically consists of technical neural networks and is characterized by using (many) multiple cascading (and possibly recurrent) processing layers.
Before the advent of cheap GPU ressources, technical neural networks tended to be relatively shallow, in terms of processing layers, due to the required processing power. Today this is no longer such a limiting factor, making deeper network architectures feasible. Hence the name deep learning.
For further reading look into Mr. Islams link to the nvidia blog-post or simply have a look at the Wikipedia-entry: https://en.wikipedia.org/wiki/Deep_learning
Deep learning is a fancy name for multilayer/stacked neural networks (and a growing set of related algorithms) to ease grant proposals getting approved.
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