As a rule of thumb, if it can be done with tools and materials that can fit in a suitcase, it's cleaning.
If everything you need can fit in a minivan, it's restoration.
If it takes a full-size room (or two) and and multi-hundred-pound power tools are involved, it's repair.
I categorize these things pretty much like George does. Cleaning, restoration, and repair are each separate but interrelated things and each step up the ladder involves aspects, either whole or in part, of the categories that fall below it. It's not wise to make a repair on a dirty pipe for example.
To take things a step further, I also break the "restoration" category into two sub-categories; restoration and refurbishment. If you're attempting to return a pipe as close as possible to its original, as-sold condition, day-one faults and all, it's restoration. If you're intentionally making changes along the way (rustication, change of color, opened airway, etc.) it's refurbishment.
I would think as long as everything is original and you are just making it look clean it would be under restoration, those things like: reaming the bowl, romoving stem oxidation (including sanding), fixing loose tenons, removing rim grime.
I put all of these things, except for the loose tenon, firmly into the cleaning category. Think of it like this: If you wash a '67 Camaro to remove the road grime, you're just cleaning it, not restoring it.
Now what about things like sanding stummel, re-staining, topping the rim. Are those repairs or still just restoration?
Could be either/or, depending upon the reasons for the work. Then again, it could just be completely fubaring the pipe.
