What is the deal with mandb and stray cats?

From the Glossary in /usr/share/doc/man-db/man-db-manual.txt (source is manual/glossary.me):

cat page
A formatted manual page suitable for viewing on a vt100-type terminal.

stray cat page
A cat page that does not have a relative manual page on the system, i.e. only the cat page was supplied or the manual page was removed after the cat page had been created.