What is stored in the "/var/lib/dpkg/updates" folder?

I've seen some folks have errors relating to files in /var/lib/dpkg/updates. All I can find about the directory is that the files in it are numbered 0000, 0001 etc. and that the error messages often mention "trouble parsing one of the files".

/var/lib/dpkg/updates folder is empty on my system, so I can't see what's in the files. I've not been able to find information about what is stored in this directory, only many forum posts and bug reports mentioning the directory.

So, what is this directory for?

During the update dpkg stores status of the installation/update there. This is how an incomplete installation process can be detected and decided what are the next packages going to be installed, So that the system can ask to use dpkg-configure -a if anything happens before completing installation or update.

Normally after a successful installation, the directory should be empty.