Pivot cup
What is Pivot cup in skateboarding?
The pivot cup is the urethane cup inside the baseplate where the tip of the hanger pivots. It sets how smooth the truck turns.
Extended definition
When a truck squeaks as you turn, it is almost always the pivot cup: a bit of wax or soap inside the cup fixes it. Over time it cracks or gets crushed, and along with the bushings it is the most commonly replaced part of a truck. A fresh one brings back a firm turn without buying new trucks.