CMO means Chief Marketing Officer
A CMO is responsible for all marketing activities of a company. A CMO you see especially with large companies that have a lot of budget for marketing. As a CMO you have to determine which media resources you bet on and at what time the best can be done. This is especially important to obtain market share, or when introducing a new product.
The CMOS Perspective: How technology is changing marketing [YouTube] I83r8dDwZEA [/youtube]