The key to Luke's turning is the moment when he and Leia realize the Emperor is no longer defined by his physical form, but has become a chaotic nexus of dark energies that swell and burst open the fabric of space, tearing apart everything in the vicinity, human and machine.---
Eager to meet his captor, Luke learned that the dark side nexus he had sensed was none other than the cloned reincarnation of Emperor Palpatine himself.
I already mentioned that individuals can seem to be nexuses and I was referring to the exact quote you posted as your second example. Regardless of if its an individual or place giving off a Darkside aura you wouldn't be able to tell unless you were actually under the effects of a nexus.
As for the first - Nexus: the central and most important point or place.
What the hell are you talking about, lmfao?
A passive amp shouldn't be expected because the full nexus is contained within the body. Passive amps are generally when a broad nexus, like a planet, amps an individual without them having to call upon the power since they are within the power. That being said, some individuals, like Revan, are so powerful that quotes have stated they passively amp those around them, presumably because their Force energy leaks and bleeds onto the environment.
No, it's just a nexus confined to a specific location (i.e. the body of a person). It's not different from nexus' locked between walls, etc.
"The Revan was here yesterday. It is a gift to be in the presence. I felt the Force - it travels below your skin, strait to the heart, lungs, the gut. A warmth and a chill."
Do you read what I type? They don't because the nexus is confined, not because the nexus is different. The temples on Yavin IV, which are nexus', also confine the dark side energies. Meaning if you are near it but not inside it, you aren't passively amped. Same applies for the body. There's no distinction.
Non-Force sensitive slave.