It includes all who have a deep interest in something or some activity.

VOA: special.2009.05.17

Some of you are sound asleep, deep in delta.

有些现在正蒙头大睡，就是δ波。

耶鲁公开课 - 心理学导论课程节选

In some places, the canyon walls are more than a kilometer deep.

VOA: special.2009.10.07

In some areas the snow is many meters deep.

VOA: special.2009.01.07