Staging Site
Also known as: test site, preview site
A private copy of a client website where you break things before the real one is involved.
You make the change on the copy. You look at it. If it is right you move it to the live site, and if it is wrong nobody but you ever knew.
Any shop that edits a live client site directly is one typo away from an awkward phone call. A staging copy costs very little and removes a whole category of bad afternoon.
A staging site is only useful if it genuinely matches the live one. A copy that has drifted gives you confidence you have not earned, which is worse than having no copy at all.