Like most internet communities, reddit has its language, which you'll be aware as soon as possible. Redditors have a tendency to talk in acronyms which includes: "op," "til," mama," "ama" ... beautifully, "op" merely describes the "initial poster" in a thread.
What is Pligg?

Pligg is an open source content management system that lets you easily create your own user-powered website.