What is an aileron bushing,and what's its use?
Bushings are a type of bearing that has no rotating parts. They are among the oldest bearings known.
There is nothing special about it being for ailerons, except that is will be installed on the hinge of an aileron.
Advantages may be, compared to one standard ball bearing: smaller diameter (easier to fit in thin trailing edge) lighter weight (great for flying devices) low maintenance requirements (brass rotating around steel axle is almost autolubricating, Teflon even better) easy dimensioning (cut at the length needed)