A jump off site is a regular campsite at a cheaper rate as you are heading into the the park the next day with your reservation. The Kiosk campground is fairly open but its usually pretty quiet. Here is the campground map that shows all the sites with photos. https://reservations.ontarioparks.com/Algonquin-Kiosk.
Depending on how late you arrive you might consider many of the great sites located on the lake not to far from the access point. Some just a quick 5 to 15 min paddle.