What are "STRONG EC's"?

People frequently say “oh, you have weak EC’s” on these blog forums; however, what is a “strong EC” for super selective schools like the Ivy’s, Stanford, or MIT? What exactly are people looking for?

There is a whole thread on this; feel free to join the discussion there. Closing this thread.
http://talk.collegeconfidential.com/what-my-chances/210497-those-ecs-are-weak-so-whats-good.html