Torque steering is an effect in front wheel drive cars caused by large amounts of torque affecting steering in such a way as to make the front wheels "squirm" (oscillate) from side to side under heavy acceleration.
This effect is noticeable to the driver by the steering wheel being tugged back and forth by the wheels.
This effect can be engineered out of front wheel drive cars, using techniques such as advanced multi-link suspension systems.
Torque steer is mainly caused by uneven half-shafts between the transaxle and wheels. When excessive torque is applied, one shaft flexes more than the other, thus causing one wheel to momentarily spin slower than the other. This causes a steering effect. Ford engineered a simple method of eliminating (or at least reducing) torque steer by expanding the transaxle a little further to equalize the lengths of the halfshafts found on front wheel drive cars.
Any car with a high output (especially turbocharged) engine and front wheel drive is likely to exhibit some degree of torque steer.
Excessive torque steer may be caused by damage to suspension/steering components, tyre defects, etc.