Basic Terms and Concepts

I know I kinda burried that at the bottom of the previous post, but now that I see that a number of my SciBlings are trumpeting it loudly (see Chad, Tara, Janet, Afarensis and Mark, so far), I guess I’ll make a little bit louder call myself.
When you are immersed in a scientific field for a number of years, it is easy to forget that not everybody undrestands the basic concepts and terms of your field. While I always try to keep that in mind, I am sure I baffled you on occasion. Does everyone know the difference between phase, period and amplitude, the difference between phase-delay and phase-advance, what the acronyms PRC and SCN stand for?
You may have noticed the link on my side-bar to the Dictionary of Circadian Physiology, where you can get a quick definition of the term you are unsure of. Or, if you have time and inclination, you can dig deeper into my Clock Tutorials archives. For stuff in biology outside of chronobiology, you may be following my BIO101 lecture notes (hmmm, I should make a separate Category for it).
The bloggers here at Scienceblogs have a large repository of knowledge in a variety of areas of science. So, if you have questions about animal physiology, animal behavior, or chronobiology, you can always ask me. If I don’t know, I can always refer you to a SciBling who is more likely to do. Pick the terms or concepts that keep popping up but you are not exactly clear what they mean and I’ll try to explain.
Update: John Wilkins has broken the ice with the very first post in this series.