If you've ever read works of theology, it's not typical to come across a book routinely cited as "Denzinger".
"Denzinger" refers to the name of the editor who compiled the Enchiridion Symbolorum et Definitionum.
This book contains a list of authoritative statements of faith, as well as condemnations of heretical propositions.
According to Wikipedia, the English version online is an older version (different versions can have a different numbering system).
Have fun.
