The creature knows the area you’re in (i.e. which square of the map you’re on), but can’t see you clearly or tell exactly where you are within that area. They can use abilities with the Area tag to affect you without needing to guess your location, but cannot target you with abilities that require line of sight or being able to see or detect you. If they use a non-Area ability targeting your square, they must Succeed on a DC 11 Flat Check or the ability automatically Critically Misses and has no effect on you.
While you are Hidden from a creature, they are Flat-Footed against your attacks.