score:11
The Catholic Encyclopedia is a public domain Encyclopedia compiled in the early 20th century. Since not a lot has changed in the last hundred years, it's a pretty excellent resource.
Beyond that, if you want something that'll overload your senses, you can check out the intratext search of the Catechism of the Catholic Church
The other thing that might come up (and hopefully not here) is that we'll use awful acronyms like LG (Lumen Gentium), DV (Dei Verbum) and CCC (Catechism of the Catholic Church) or CCCC (Compendium of the Catechism of the Catholic Church) to reference some important texts or encyclicals. For these I've only seen good glossaries for these in the backs of print books, like the Catechism, and not a complete list, just the ones referenced within, but in the Catechism that's like everything from the Apostolic Father's on.
Finally, I just found this site http://www.catholicreference.net/ so I'm super glad you asked because I'm going to link to it all the time from now on!
Upvote:5
This looks like a really good place to go to learn about Catholicism and it looks rather expansive. I would imagine that it would also be a really good and useful tool for looking up a lot of generic religious terms. The articles seem to be rather expansive and exhaustive.
Upvote:6
Catholic Answers is a great reference site as well. I have found many answers in their public forums. They are usually moderated by well-known apologists.