Simply put, a ball joint is a ball-shaped (usually called "spherical" by automotive pros) bearing that connects a control arm of your vehicle's steering knuckles (which are connected directly to the wheel assembly) to the automobile's suspension system. Because ball joints allow for a decent range of motion, they can help transfer the input you give by turning the wheel -- also known as steering -- to the wheels themselves even as the car bounces around over potholes, debris, speed bumps, and so forth. Because the ball joint flexes about, the car remains under control even as the suspension system moves up and down while mitigating the jostling caused by road and driving conditions.

Without a ball joint, your car's shock absorbers would be essentially pointless and your car would be as rigid and rickety as a horse-drawn carriage from centuries past. The location and responsibility of the ball joint also sees an exceptional amount of pressure put on this diminutive component, so ensuring that all the ball joints in your vehicle are in good repair and working properly is of immense importance for safe driving.