The phrase "wheel cylinders" refers to parts of a vehicle's braking system that help in applying pressure to the brake shoes, which eventually enables the vehicle to slow down or stop. Full definition
My car's brakes were inspected some time ago, and it was found that the passenger wheel cylinder for the rear brakes was leaking. (mechanics.stackexchange.com)
I found a very very slight leak in wheel cylinder in right rear drum drum brake. (mechanics.stackexchange.com)
It features 4 - wheel drum brakes and new wheel cylinders, master cylinder, fuel pump and battery. (barrett-jackson.com)