Ventral
From Memory Alpha, the free Star Trek reference
Ventral refers to the underside of a body and the term is commonly used in defining the bottom of a starship. This nomenclature is necessary while functioning in the three dimensions of space.
During Shinzon's attack on the USS Enterprise-E in 2379, all ventral phasers were fired in a single maneuver. In addition, the starship's ventral shielding failed on deck 29 as the result of a focused attack. (Star Trek Nemesis)
