reclining is all it means--
when sitting on butt for hours on end, a simple consideration of mechanics would conclude that if one could reduce the vertical force upon one's back, and butt, the less pain and resultant discomfort and after years, malfunction of lower back and hip area.
i find that only after 4 hours, i must stand up, if only in the flight deck. and that is only on the 737-800.