What does "locked for Shared Use" mean, exactly?

The file is open by you or someone else in a browser. I found this out because had the file open in a different tab for viewing and comparing changes I was making.  As soon as I closed the tab thus closing the file I was able to upload my changes.  I tried it twice because I couldn't believe it.

That's possible but if you read some of the many complaints about this issue, you'll see it can occur when the file isn't open anywhere. And even if your suggestion were correct, Msft still needs to apply a fix because locking a file that happens to be open in a browser somewher e is absurd and obviously not intentional, according to Msft's own documentation. They state that a file recently closed may need "some time" to be available again. The problem is people have experienced severe delays (hours in my case) before they can access a file which is an indication of either a bug or a chronically flawed design. Either way it needs to be fixed and not ignored as it has been so far.

@Tisky - Original post issue has not 'gone', it times out after a certain amount of time, this is one of the underlying problems...the time it takes for the file become 'unlocked'.  It seems to take anywhere between 1 and 10 hours, I personally experienced this by patiently waiting over an hour last week to see how long it would take. 

Clearing cache and credentials manager does not fix this issue, neither does rebooting, nor signing out of Office 365, or even signing in using InCognito/InPrivate mode.  

I have seen some online posts talking about a 10 minute lock, but that was from development documents found on Github.

I'm opening a support ticket with Microsoft and will post their response here.

Is Microsoft going to chime in again or are they considering this thread closed?

This issue is a big problem for my users as well and would love to see MS look into this.  I'm creating a support ticket with Microsoft Support and will post any response from them here.

@Tisky - Original post issue has not 'gone', it times out after a certain amount of time, this is one of the underlying problems...the time it takes for the file become 'unlocked'.  It seems to take anywhere between 1 and 10 hours, I personally experienced this by patiently waiting over an hour last week to see how long it would take. 

Clearing cache and credentials manager does not fix this issue, neither does rebooting, nor signing out of Office 365, or even signing in using InCognito/InPrivate mode.  

I'm opening a support ticket with Microsoft and will post their response here.

I am adding my voice as an admin on behalf of my users. This issue happens when they tend to work quickly with Word documents on SharePoint. I am also planning to open a support ticket, but would love to hear more about what's happened with yours @Pistolbrazil.

FYI: I opened a ticket with Microsoft support over this issue expecting that it will be affecting us a lot next month during our busy season. Our users get tripped up a lot with this if they open from SharePoint into Word Online and then choose to Edit in Word.

I was given some suggestions on ways to work with files that would prevent locking:

1. Right click or select and choose open in Word (eliminate the step of opening in Word Online)
2. Pin the folder location where the files are saved in SharePoint into the Word client. Open directly from the Word client.
3. Check out the files to work with them, and then check them back in.

We were also told that if a file has a lock that absolutely will not release, to download a copy of the file to work with it and then re-upload it when finished.

Not a concrete solution, but some helpful tips from Microsoft. Maybe it will prevent a headache for one of you. Here's hoping they hear our loud and frequent complaining on this issue!