the term 'deep web' refers to the subset of internet-connected information that is not widely published eg on search engines, where as the 'dark web' is specifically sites that hide their hosting information behind tor i2p etc

as unfair as it may be, a huge part of the usefulness of information is its accessibility, and these search engines currently hold a near-monopoly on which sites can generally be considered readily accessible, ie the 'surface web' above the deep web

I would personally call telegram/viber/whatsapp/et al. groups/chats/channels "dark web", since information is not indexed there and is basically decaying over time. In about a decade or decade and a half ago, forums flourished, it was really easy to find and share relevant information with relevant group of interested people. I particularly was interested in car's DIY service & retrofit topics. Unfortunately everything is mostly in messengers these days, which won users by offering real-time responses, but providing no real way of topic sorting or proper history. Duplicates of questions and answers of different topics and threads mixed together into an information garbage bin.