This articles explains the difference between an Event and Reservation.
Reservation: A reservation is a booking for one court at one instance in time. For example, if you a user books Court #1 at 1pm on Saturday, that is a Reservation.
Examples may include: A ladder match, a private lesson, etc.
Event: An event is a special kind of reservation that can be one or more days, and can be signed up for.
Examples may include: Beginner Clinic, Adult Mixer, etc.
It's important to note both Reservations & Events can be categorized by setting up Reservation Types and Event Categories under Setup.