Since the subject comes up from time to time, it is useful if everyone applies the terminology correctly. I dug around and found a pretty good explanatory article here.
For anyone who took psychology, this is not new news, but with the current popularity of "all positive" dog training, it's useful to understand where it comes from. B.F. Skinner's work is hardly new or modern, but it is certainly in vogue these days! Unfortunately it is also frequently misunderstood or misinterpreted. Understanding the basics is helpful when you are observing how an animal is reacting to your training methods, and can help one make good decisions about both reinforcement and punishment. IMO, many people make the mistake of not moving to a variable reinforcement schedule once a behaviour is established. Anyhow, I hope the article is helpful in clarifying the terms and the science behind them.