Cover

Cover is a defensive combat move used by Noctis. A visual cue will sometimes appear when standing near a large object/wall, and Noctis can take cover by pressing / when the cue appears (not all objects/walls can be used for cover). Standing in cover allows Noctis to regenerate HP and MP faster.

In Episode Prompto
The cover ability is expanded upon in Episode Prompto, wherein Prompto can both crouch behind objects (to avoid an enemy attack and/or to spring an attack from) and walk while crouching by pressing (not tapping) / long enough for him to crouch (the button can then be released). Tapping the button again will cause Prompto to roll-dodge, and firing a weapon will immediately take him out of cover. When playing as Prompto, the player does not need the same visual cue as is required for cover when playing as Noctis.