From the PHB, Appendix A on Conditions:

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> INVISIBLE
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> * An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature's location can be detected by any noise it makes or any tracks it leaves.
> * Attack rolls against the creature have disadvantage, and the creature's attack rolls have advantage.
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One of my players was sneaking around while invisible. Unfortunately, his Stealth roll failed to beat an NPC's Passive Perception, so he was detected. What does 'detected' actually mean?

I ruled at the time that the NPC could tell someone was there but not exactly where (because she heard the noise made by someone moving), but RAW, did she know exactly where he was?