"Clean file/folder" attempts to clean any infected files it finds. If a file cannot be cleaned, it will be marked as such and you can then take appropriate action.
A broken file/archive/etc. are files that you would normally not be able to run. This includes corrupted zip files, etc. The documentation from Kaspersky says:
Kaspersky wrote:To use redundant scanning, for search of viruses in the damaged and spoiled files. Slows down process of scanning many times over. It is not recommended to use.
Unknown errors occur when the virus libraries returns to us and gives an error code that is not known. This could be because the file was in use at the time, etc. but essentially means we were unable to verify that file.