Plain English Meaning
The front wheel can spin freely from side to side. The pilot turns the airplane by braking one main wheel harder than the other, not by steering the nose wheel.
Full Definition
A nosewheel that is not mechanically linked to the rudder pedals and is free to swivel left or right on its own. Directional control on the ground is achieved by using differential braking on the main wheels, and sometimes by rudder effectiveness from propeller slipstream, rather than by steering the nosewheel directly.
Context Anchor
Seen in tricycle landing gear discussions, especially when comparing airplanes with steerable nosewheels to airplanes that use free-swiveling nosewheels.