Aware Of Presence
When you are aware of another creature’s presence, you don’t necessarily know exactly where it is. Typically this occurs when the hidden creature has taken some action that revealed its general presence in the area but has successfully used Stealth since then to hide its exact location. If you have succeeded at a Perception check to notice a creature with an imprecise sense other than blindsense, you are aware of the creature’s presence (if you have blindsense, a successful Perception check means you are aware of the creature’s location; see below). You cannot directly attack a creature if you are only aware of its presence, but it is subject to area effects affecting its location.
In order to directly attack such a creature, you must pinpoint its exact location with an additional Perception check to search (see page 144). If this check is successful and you are using an imprecise sense to pinpoint a creature, you become aware of the creature’s location (see Aware of Location below). If this check is successful and you are using a precise sense to pinpoint a creature, you are observing the creature (see Observing below).
Source
Core Rulebook pg. 260