I disagree partially with the above opinions.
To me overtraining is very easy, especially for those who are overly-motivated to lift and get stronger. Like the newbs that lift chest 5 days a week, and wonder why the muscle isn't growing. Lifting causes damage, we all know that. It's the repairs that make the muscle bigger and stronger. Too much damage though, and the muscle doesn't get a chance to ever recover.
I don't think saying it's the same as undereating is a good thought, mainly because if someone hears that, takes it the wrong way, then they start eating the wrong food, just to keep eating for calories.
Mt Snow, VT - May 5, 2012 - Completed!
Gunstock, NH - June 1, 2013 - Completed!
...i remain, he who remains to be...