Which of the following is the best definition of "nocturnal"?

The term "nocturnal" refers specifically to animals or activities that occur at night. This definition captures the essence of what nocturnal means, as it denotes a lifestyle or behavior that is primarily active during the hours of darkness rather than during the day.

The other options diverge from the correct meaning: one indicates daytime activity, another implies a peaceful state, and the last relates to forms of communication. None of these capture the essence of being active at night, which is the core concept behind "nocturnal."