From the names, I would guess that is optimization, that is marketing. Marketing involves actively promoting your product;service using coupons, digital marketing methods, discounts, promotions, giveaways, etc. Example using twiveaway.com would be SEM but not SEO. Keyword research and optimization is SEO and not SEM. Facebook fan page creation is SEM and not SEO because its intention is to gather people and sell to them.
They are both internet marketing ways but SEO is broader and aims to gain organic traffic.SEM is under the umbrella of SEO
The Social Media Marketing is more a brand building and customer relationship activity while the Search Engine optimization is more about sales and marketing. Mehta Inc (mehtainc.com) Internet Marketing company
SEO is a method of improving ranking in SERP's and traffic through on-page and off-page. SEM has a wider definition SEO is a part of SEM. SEM is directly related to marketing, its a way of promoting your business its also called e-marketing, online marketing, internet marketing. This involve various methods such as PPC, CPA, CPM, and adsence, adwords affiliates etc.