Did some searching, here's what I came up with. Note: The picture was stolen from BRP's site.
Triple clamp offset is how far forward a line between the two fork tube centers is from the center of the steering head, as viewed from the top. See the pic for offset.
Rake is the angle between the headset tube and a vertical line. Increasing the rake will move the front tire farther from the bike. Rake is measured in degrees, and is a frame specification. To visualize trail, draw an imaginary line along the path of the headset tube to the ground. Measure from this point to the center of the tire patch. This is trail, and is measured in inches.