what is the the rail that goes over the keys and has to removed to remove the keys called? It's not shown in any diagrams I have found.

I usually refer to it as the up-stop rail. But, I've also heard it called the fall strip.

Perhaps there are other names?

key stop rail

I know some terms are completely different over here in the UK, but we call it the "Name Board" - I'm not sure, but I think it comes from years ago when makers put their names on this rather than the fall.

Here is a more complete diagram of Grand action. https://www.pianoparts.com/grand/

It says its a "Key Stop Rail" so I suppose that should be the convention but I have heard up-stop rail used in my part of the country.

Greetings,
The upstop rail is usually the rail that limits the underlever's motion. The key stop rail is usually that rail that keeps the keys in place during cartage.

Therefore, some people call it the "Key Upstop Rail". I have heard the rail that Ed refers to called the "Damper [Lever] Upstop Rail".

I have also heard the subject in question called the "Shipping Rail" because it really serves little useful purpose other than to keep the keys in place when a grand piano is put on its side for shipping. It probably won't be missed until then but if it is absent, the keys may fall out of place and require a service call from a technician to get them back where they belong. I have performed any number of those service calls over the years when a technician neglected to re-install the rail.

Having said that, there have been instances where I could eliminate the "klop" sound from quickly released keys simply by adjusting the Key Upstop Rail to a close tolerance. The felt on the rail prevents the key from bouncing and therefore cuts down on some of the clatter it may make. This will sometimes work in both grands and verticals.

Care must be taken, however to make sure that the rail is not actually pressing on any keys. If you see an uneven key level, this is the first thing to check. If the Key Upstop Rail is too low, it may be pressing slightly on some keys and make them appear to be unlevel.

I have heard it mentioned that extremely agressive stacatto playing can flex the key above the balance rail bearing and when it unflexes the force can propel the key upwards and the key upstop rail will prevent the key from riding up the balance pin or klunking back against the bearing.

I have never been able to do it with a wide setting or the rail removed so I'm not sure how much truth there is in it.