Bearings allow rotation of one part relative to another. They come in many different sizes and shapes, with different properties. Ball Bearings
are used on cars, boats, skate boards etc. They work, but they give friction, and require maintainance- they need adjusting, greasing, they wear out.
In contrast, let's try to imagine the ultimate bearing. A bearing that never wears out, and can spin at incredible speeds with even less friction than a ball bearing; and can take incredible force without disintegrating. Never needs maintainance, never needs adjusting.
Hydrostatic bearings can do all this and more.
A Hydrostatic bearing uses a sort of hovercraft effect. A pump puts a lubrication fluid of some kind (even air will work) in between two flat metal surfaces at high pressure through small holes. The two surfaces are kept apart by this and can spin independently. Because the fluids used have low viscosity very little drag is produced. Enormous rotation speeds are possible, 100,000 rpm in some cases. And, because the two surfaces don't touch, no wear occurs.
Hydrostatic bearings are used in the latest Space Shuttle Main Engines. They've also been used on LARGE telescopes, where the bearing is able to deal with the extremely high weight and deliver incredible stability.
They haven't made much headway into more general use yet. But there's no reason that cars can't use them and get better miles per gallon, with improved reliability. Ok, no reason, except that the car manufacturers want to carry on making lots of money from replacing your engines ;-)
Anyway, hydrostatic bearings are cool tech.