Canned Tune: Generic tune that comes with the tuner, customized from other models of the tuner for your model, but generally not the best you can get for your specific vehicle.
Custom Tune: After installing the tune, you "data log" with the tuner and send the information into a tune writer such as Hemifever, and he writes a custom tune (not canned) more specific to your vehicle and its add ons.
Dyno Tune: You hook the truck up on a Dyno and get real information right there, and build a tune specifically for your truck off the information the dyno is putting out (A/F ratio, HP, TQ, etc.).
Both Custom Tune and Dyno Tune are "Custom", but one you data log yourself and send off to somebody to work on, while the other you take to a local shop that specializes in such and custom tune it right then and there.