Second startup I hear phrasing it as "no ego". I get pedantic on that word choice. I think "don't be an asshole" is way more accurate :P. For example, I have a very strong ego (ego is defined as high self-esteem, high self-importance), but I always admit I know nothing about something, or that I'm wrong, or that someone made a valid point that trumps me, or I've made a mistake, etc. In fact, I'd even say that it feeds my ego to do these things.

But this concept of open-mindedness is hard to phrase in a catchy way like "no ego", admittedly.