Champion "closeness"
J4's W gains a bonus for each nearby enemy champion. Someone told me that "nearby" means enemy champions close enough to be hit by his W's slow, but I figured if that were the case they would just say that. Does "nearby" mean within your vision range? do they need to be visible?
Other stuff like the "Assassin" mastery and "Legendary Guardian" also have "nearby champions" in their description, but it's not very clear what nearby means. I think Riot should list a range in these descriptions especially since it might be different for different effects.