Subsequent versions of an assembly that differ only by build or revision numbers are considered to be Hotfix updates of the prior version.
This section explains the difference. The Revision is used when your product has shipped and you need to make fixes to a shipped version while you are already progressing with updates.
For example 1.1.10.0 ships. I am making small changes to functionality and am at 1.1.20.0 when I get a security alert that needs fixing. I can’t increment 1.1.10.0 to 1.1.11.0, as that represents something else. So I use 1.1.10.1 to identify it is a revision of the 1.1.10.0 code.
Hope this is a little clearer than mud. Also remember the size of the company and the size of the software projects they ship that came up with these definitions.