Yes, Delayed Onset Muscle Soreness. It can make you feel like staying perfectly still until it goes away, but in actual fact the best thing to do is get moving. You'll be meuch sorer and the soreness will hang around longer if you stay inactive.
You want to try and do similar training to the one that made you sore, but at a much lower intensity and duration. Quite often when I get really sore with weights I'll go and do the same exercises but lift much less weight.
If it has come from bodyweight exercises such as squats or push ups just go for a walk to loosen up. Bike riding can also be quite good.
I do have to laugh though. When you're starting out you absolutely hate that soreness, but when you start really getting into your training you actually look forward to it ![Confused [8-)]](/forums/emoticons/emotion-43.gif)
Ray
My new book:
Winners Do What Losers Don't