“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.”
SEM is also known as Pay-Per-Click (PPC) advertising and the most popular vendor is Google AdWords. SEM allows you to, more or less, instantly place your ads in front of people seaching for keywords you specify, creating pre-qualified traffic.
The amount you are prepared to pay or bid for a click determines your ad’s position within Search Engine Results Page (SERP).
This is an excellent way to drive instant traffic to your website but requires careful planning and execution in order to convert this traffic to sales or other actions of value.