Prof. Stephen Boyd, of the Dept. of Electrical Engineering at Stanford, briefly explains what NP-hard means.

This clip was taken from the Prof. Boyd's class "EE364a Convex Optimization 1" and can be found at:
http://www.stanford.edu/class/ee364a/

The complete version of this specific lecture can be viewed at:
   • Lecture 1 | Convex Optimization I (St...