[thoth]

I'm not sure Microsoft gives an official name for "\\?\".

The closest I can find is "To specify an extended-length path, use the "\\?\" prefix." (from https://msdn.microsoft.com/en-us/library/windows/desktop/aa3...).

So maybe it is the "extended-length path prefix".

[cataphract]

You can also use that prefix to access volumes that have no mount point, as in \\?\Volume{<UUID>}, among other things like UNC paths (\\?\UNC\...). So that's not a good name.