Alignment

This playlist has a lot of great videos explaining suspension geometry and is a great starting point for learning about FSAE vehicles. 

Scrub Radius

The distance between the center of pressure of the tire contact patch and the intersection of the steering axis with the ground when viewed from the front. (see image above)

This is the moment arm by which tractive/braking forces are transmitted to the steering axis.  For the rear suspension, it's a good idea to have the steering axis intersect the ground at the center of pressure of the contact patch in order to reduce the moment that will have to be reacted by the suspension links. 

Mechanical and Pneumatic Trail

The distance between the wheel center line and the intersection of the steering axis with the ground when viewed from the side. Since the center of pressure is slightly behind the wheel center, a tire also has pneumatic trail. 1" is a good baseline value to use for pneumatic trail. Total trail = mechanical trail + pneumatic trail. 

Total trail is the moment arm by which lateral forces are transmitted to the steering axis. Pneumatic trail tends to decrease as the tire reaches its peak of grip, which gives the driver an indication that the tires are at their limit.  See: Race Car Vehicle Dynamics, Chapter 2. 

The image below is and example of positive mechanical trail. Positive trail creates a self-centering effect on the steering system. Trail should always be positive for the front wheels.  If trail is negative, lateral forces will cause the wheel to try to reverse it's direction and make the car undrivable.