Node.js provide an efficiency in doing nothing?

I heard a speaker described Node.js as a webserver that "efficiently does nothing". I thought it was a joke but others looked to nod agree开发者_运维百科ment. Can someone explain my misunderstanding of this phrase?

I think this is a reference to the nature of node's evented and non-blocking architecture. While waiting for a process to complete and/or return, node doesn't block another process from work.