In this letter, Jeff details why free cash flow per share is the way Amazon measures the value it creates. It's worth reading the letter instead of listening to it because he provides some illustrative tables. 

This letter pairs very well with Warren Buffett's Berkshire Hathaway letter from 2007 that discusses Returns on Invested Capital. 

2004 Amazon letter

2007 Berkshire letter

Also sorry if there's a little bit of skipping. Don't know the cause but I tried to edit out.