Underlined words defined?

I've noticed a few forums (including this one) underlining certain words and providing a definition. (example = SEO)
How can I get this on my forum?

Sorry if this is obvious or a really nooby question, but I can't seem to find it in any searches.

 

This is a vBSEO feature. There may be a modification at vB.org that can offer this functionality. A search yields this thread: Acronyms for vB - vBulletin.org Forum.
I'm not sure if it works, or if it does exactly what vBSEO does, but you may want to look into it.

Thread moved to Forum Software.

 

Thanks for the help!

 

I remember seeing a mod that allowed you to build a glossary of words, and I believe it allowed you to underline and link them to the definition as well.