Here's a few of mine:
Apathy Syndrome-
Mysterious disease that has supposedly struck the Bay area. But in reality, Shadows are the cause.
Dark Hour-
Occurs every night at 12:00. No machine will function expect those made especially for the hour.
Transmogrify-
During the Dark Hour, those without 'the potential' turn into coffins. One feels nothing in this state and is unaware of the Dark Hour.
Potential-
The power to summon a Persona. Those with Potential can experience the Dark Hour without being Transmogrified.
Persona-
The embodiment of one's inner power. According to Igor, a Personas' appearance reflects one's personality.
Social Link-
A bond made with another person. Getting to know others is the key to strengthening your personas.
Shadow-
Monster that appears during the Dark Hour and preys on those who are conscious. It's victims become 'The Lost'.
Evoker-
Enables the user to summon a Persona although it is supposedly possible to do so without one.
Full Moon-
Just as Pharos said, on a night such as this, you will face a powerful Shadow.
The Voice-
If one hears the Shadow's call, one will be drawn into the dangerous Dark Hour rather than be Transmogrified.