This terminology has plagued the piano industry as well.

First and foremost is ego.  A technician wants to use the word
'rebuilt' for personal enhancement.

Second is the customer's misunderstanding.  Although they have been
told that minor repair or reconditioning has been performed, in their
eyes (ears) the change is so dramatically different that they bestow
the term 'rebuilt' to describe the transformation.

Some techs call restringing 'rebuilding'; it is not.  Replacing the pin
block is not rebuilding.  It is not until the sound board is replaced
(not repaired) can it truly be called 'rebuilt'.  Anything short of a
new pin block and sound board is reconditioning.

New hammers does not constitute action rebuilding.  Rebushing keys,
replacing all action parts is rebuilding.  Most often overlooked in
action work when replacing hammers is the change of hammer weight.
Each hammer will have a different weight from the original and thus the
factory key leading will not be appropriate.  There is a wide range of
touch weight which goes undetectable until it is corrected.

In my shop is a piano which was purported as "Completely Rebuilt" in
1986.  it was refinished, restrung, new back and board, new hammers and
new key tops.  But it still had the original shanks & flanges, wippens
and underlevers.  I would consider this to be a misrepresentation.

The first thing I did was to replace the backaction (underlevers) and
hammers/shanks/flanges.  It is playing well and the wippens will
remain, I recondition them.

I will sell it as a "used piano" which had a new board, block,
restringing, refinishing in 1986, and, with the above action upgrades,
"reconditioned."

Jon Page, piano technician
Harwich Port, Cape Cod, Mass.