Since the concept of being below is itself somewhat vague, scientists define the nadir in more rigorous terms. Specifically, in astronomy, geophysics and related sciences (e.g., meteorology), the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location.
anatomical dead space. In pulmonary physiology, the area in the trachea, bronchi, and air passages containing air that does not reach the alveoli during inspiration and is not involved in gas exchange. This is termed dead space because the air does not reach the alveoli and is not involved in gas exchange. Normal anatomical dead space is 2.2 ml/kg or 1 ml/lb.
Geek Feminism Wiki. Safe space. Safe space is a term for an area or forum where either a marginalised group are not supposed to face standard mainstream stereotypes and marginalisation, or in which a shared political or social viewpoint is required to participate in the space.