"Judgmental oversteering" means to intentionally not follow the taxiway centerline when turning. It is a technique used on large aircraft to turn on tighter or smaller taxiways.
In a sense, it is like driving a long vehicle, such as a truck or a bus. Instead of following the lines on the road, the driver would deliberately overshoot the entry of turn, i.e. delay turning the steering wheel. This technique allows the rear wheels to stay on the road instead of going over the corner which may have fences, poles, pedestrians or other obstructions.
Here is a drawing from the 747x Quiet Longer Range Family Airport Compatibility document which illustrates the tracks of each gear for the "judgmental oversteering" and "cockpit centerline" methods:
This FAA document about airport design summarizes the pros and cons for each method (p.52 of PDF, p. 34 of document):
Cockpit Over Centerline. Taxiway intersections designed to accommodate cockpit over centerline steering require more pavement, but enable more rapid movement of traffic with minimal risk of aircraft excursions from the pavement surface. (...)
Judgmental Oversteering. Taxiway intersections designed to accommodate the judgmental oversteering method of maneuvering require the least pavement widening. However, judgmental oversteering requires complex maneuvering, increases the risk of aircraft excursions from the pavement surface, and slows the flow of traffic.