Search Engine Marketing and Search Engine Optimization are often used interchangeably, however they are two similar but different aspects of Internet marketing.
Search Engine Optimization involves optimizing web pages to ranking naturally (organically) in Search Engines.
Search Engine Marketing refers to marketing your online business using PPC advertising (pay-per-click) on Search Engines.
Google Adwords usually comes to mind with Search Engine Marketing (SEM).
Based on your bids and quality score, your ad will appear in sponsored listings along the right hand side and on top of all the natural search results for Google. Your ads will also be syndicated on other Search Engines and websites within their network as well.
Stay tuned for more details and resources to enhance your SEM and SEO initiatives.
Wish you the best,