Hidden layer is a term of art in machine learning / neural network research. See https://en.wikipedia.org/wiki/Hidden_layer https://en.wikipedia.org/wiki/Hidden

Hidden layer is a term of art in machine learning / neural network research. See https://en.wikipedia.org/wiki/Hidden_layer https://en.wikipedia.org/wiki/Hidden_layer . Somehow this term mutated into "hidden state", which in informal contexts does seem to be used quite often the way the grandparent comment used it.