When a DnB head says a track is "deep", they could mean three different things. Context usually disambiguates but if you are new to the conversation, the ambiguity can be confusing.

Deep as in sub-bass-heavy

The most literal meaning. A track has heavy sub-bass content that fills the room with low-frequency weight. Any sub-genre can be deep in this sense. A jump-up track with massive subs is "deep".

Deep as in minimal or atmospheric

The Exit Records / Autonomic meaning. Sparse, contemplative, more concerned with mood than dancefloor impact. A "deep liquid" track is usually this meaning, not the sub-bass meaning.

Deep as in obscure

When a DJ refers to "deep cuts" in their set, they mean rare or underground tracks that the average listener will not know. Nothing to do with the actual sound; everything to do with the catalogue position.

How to disambiguate

Listen for context. "Deep sub-bass" is the first meaning. "Deep and minimal" is the second. "Deep cut" is the third. When in doubt, ask. Nobody minds clarifying.