Applied to steering, this term refers to the distance that the rack moves in a horizontal plane when the pinion is turned. Specifically, it correlates to the amount of area in which the teeth are cut on the rack. The rack can travel only as far as there are teeth cut on the rack, keep in mind that the rack does not have to travel that full distance.
It is a Steering Gear system in which a pinion on the end of the steering shaft engages with a horizontal rack, the ends of which are coupled to the steering arms by tie rods.
Bump Steer is a condition that occurs when your wheels have a toe change when they leave the pavement (such as hitting a bump). If a rack and pinion has the inner tie rods that are spaced wider apart than the stock configuration excessive bump steer can and will occur.
There is an urban legend of sorts concerning what bump-steer is. Some guys believe that bump steer is the vibration or shaking that you feel when you drive. This is incorrect.
The easiest way to verify if a rack and pinion kit will or will not create Bump Steer is to measure the inner tie-rod sockets on a rack and pinion kit to that of the inner tie rods on the factory center link.
Company spend a great deal of time and effort designing and manufacturing rack and pinion kits to assure that work with the factory front-end parts. It would be much easier and cheaper for company to simply use an off-the-shelf gear and shorten it.
This is the dimension between the pivot points of a steering system: the arc that the inner and outer tie rods move through should be the same as the arc that the control arms move through. The center of the pivot on the driver side to the center of the pivot on the passenger side gives the ball center dimension It is vital that the ball center match the steering geometry of the front suspension.
Standard is fine. Some people like to use synthetic.
Here is a step by step walk-through.
Looking at a vehicle from the front, the Camber is the angle that the tires lean at vertically. Positive Camber means that the top of the tire is angled away from the vehicle. Negative Camber means that the top of the tire is angled towards the vehicle.
Looking at a vehicle from the side, Caster is the angle of the steering axis line relative to vertical. Positive Caster means the top of the steering axis line is angled towards the rear of the vehicle. Negative Caster means that the top of the steering axis line is angled towards the front of the vehicle.