A term commonly used by DJs to refer to the busiest period of a night at a gig, whether it's a house party, club event, or rave. It's the time of night when the crowd is the biggest, and the DJ is spinning the most popular, energetic, and dramatic tracks (colloquially, "anthems", "bangers", and "choons"). It is usually also the time during which the headlining DJ is on the decks.
By association, it can be used to describe the tracks that one would play during this period, and record labels will often advertise a release as being a "peak hour tune" to increase the hype around the record.
People waving their hands in the air, drinks spilling, sweat, whistles, yells, and huge musical buildups are all strong signs that peak hour is arrived.
Not dancing during peak hour, or worse, leaving before it, is to be highly frowned upon.
"We got to the club just before peak hour."
"I played a set of electroand then dropped some tech house tracks at the start of peak hour."