Mobile SEO is a part of mobile search marketing, which is a part (along with mobile search advertising or paid search) of mobile marketing.
See the Mobile Marketing Association’s Intro to Mobile Search for a good overview of how natural search fits into the overall mobile search opportunity.
This mobile SEO FAQ is a work in progress that depends on community input. Please contribute your thoughts to the comments section. The body of the post will be updated periodically with the best insights, and your contributions will be recognized in the contributors section of the FAQ.