It’s at least what they sound like when unicyclists are performing koosh-koosh. Koosh-koosh is a variant of backwards wheel walking with one foot in front of the frame and the other behind. You push backwards with the foot behind the frame and use the front foot in gliding position to hold the wheel in position while the back foot is out of contact of the wheel moving forward to reposition for the next push.
The trick is so named because your feet make a koosh-koosh noise on the tyre when using this style of backwards wheel walk.
Note many people find koosh-koosh an easier form of backwards wheel walk than doing it with both feet in front of the wheel. It also has the advantage that it can be performed standing up.
I’m kinda partial to something like “Bicyclist: A unicyclist still in training wheel.” But it is a little provocative. Not self-deprecatingly British at all.