The Players' Guide to the Cities/Glossary
As is common with many games, City of Heroes and City of Villains have evolved their own vocabulary over time. Many terms are borrowed from other games. Some are unique to the history of the cities. Odds are that more than once during your time spent in Paragon City or the Rogue Isles you'll encounter terms or acronyms that you will find unfamiliar. Fortunately, Paragon Wiki already has an entire list of definitions to help you understand what your fellow players are talking about.
A list of definitions for terms in the City of Heroes and Villains universe can be found here.