Search engine marketing, or SEM, is a form of Internet marketing that seeks to promote websites by increasing their visibility in search engine result pages (SERPs) through the use of paid placement, contextual advertising, and paid inclusion.

Search Engine Marketing (SEM) generally covers two areas: Paid Search Advertising and Organic Search Optimization.

Google Pay-Per-Click (PPC) is the most popular or well known method of advertising your products and services on the Internet as it can bring you to the top in the search pages, but at a price. Even though PPC is one of the best forms of advertising, like all advertising, your exposure stops when your budget runs out.

With organic search, once you achieve a page one Google ranking you will begin to receive up to 75% more visitors to your website than with traditional Google PPC.

Source: Make sure your company is visible on Google with Search Engine Optimization