Every ship in Star Citizen has a deflection value for each damage type - physical (PHYS) and energy (ENER). A weapon's alpha damage (the damage dealt by a single hit) has to exceed that deflection value before any damage gets through at all; hits below the threshold are deflected entirely, while hits above it penetrate for their full alpha damage. This gate applies per damage type, so a ship can be vulnerable to ballistic weapons while still shrugging off lasers, or the reverse.
Selecting a weapon and a ship above populates ALPHA VS with that single-hit result and DPS VS with the weapon's sustained damage-per-second once the deflection gate is accounted for. The PREY checkbox filters the ship list down to hulls the selected weapon can penetrate; PREDATOR does the reverse, filtering the weapon list down to everything that can penetrate the selected ship.