Isolate the bearing? Other terms?

Isolating the bearing is a practice used when using a bearing guided bit with the fence. All it means is setting up the fence so that it an the bearing are in exactly the same plane. This gives you the full cut of the bit, while using the much greater supporting area of the fence instead of the bearing on the bit as a guide.

Staying on the cutting side of the bit is a safety issue. If you are making an unbalanced cut, like a rabbet or another edge treatment, you want to make sure that the only portion of the bit that is engaging the work is the "cutting side". If you can look at your bit, and see the face of the carbide insert in the flute, that is the cutting side. If you see the back of the flute, that is not. Sounds simple enough, but if you try to take too big of a cut, you can get into an unsafe situation. Staying on the cutting side puts the force of the router bit back against your feeding pressure and up against the fence. If you get off the cutting side, the bit can climb cut and steer your stock where it wants to go. This can pull your stock or your hand feeding it through the router.

Hope this is an adequate definition, I'm sure others will be able to amplify.

Have you ever cut a dado with a hand held router? If you happen to have a plywood bit, you would not have to worry about the "cutting side of the bit", as the dado matches the plywood's thickness. However, some places ie. In Canada where I live the plywood is in metric thickness (17mm or 19mm) and the standard router bits do not match this thickness. To overcome this, a well known woodworker Nick Engler, devised a "not quite so square custom base plate" that had a zero side, a side 1/16" closer, a side 1/8" closer, and finally a 3/16" closer cut. This allowed him to cut a dado to fit the plywood with 2 cuts of the router with a fixed clamped fence, simply by turning the router to the appropriate side of the base plate. To make a short story long, which side of the base plate you started (ie. the fartherest cut away from the fence with the second cut closer) allowed you to push the router away from you as you are on the cutting side of the bit. However, if you cut the first pass with shortest side of the base plate, then the second cut required you to start on the other side of your workpiece and move the router towards you, or you moved to other side of the workpiece and pushed toward where you started, other wise you would be on the "wrong side of the bit".