A spinning beam is a piece of kit sometimes used while performing suspensions. It is essentially a see-saw that can rotate, with one person suspending from each end.
Spinning beams are usually between 4 and 10 feet in length, and are hung from a swivel in the centre. Swivels are also attached to each end and then to a Suspension Rig, from which the suspendee will hang. As the people suspending are often of different weights, the beam can be adjusted to compensate for this and allow them to balance. This is done either by adding weights, or by moving one of the outer swivel fixings relative to the centre.
Depending on the surroundings, and the type of suspension chosen (most people usually go for a Suicide Suspension, suspendees are able to kick off the floor or walls to influence their own motion.