Paid search refers to any search process where results are dictated by payment from advertisers. However, many associate the term paid search with pay-per-click (PPC) advertising, a specific kind of business relationship where advertisers pay search engines or other Web hosts when ads are clicked, which gives the host entity incentive to display the ads as search results.
Techopedia explains Paid Search
Paid search is often contrasted to organic search, or search results that aren’t based on any commercial arrangement. Organic search results are "natural" or "real" in that they are based on an algorithm designed to deliver the most relevant and useful results to users. Paid search results, on the other hand, are skewed by a contractual promotion plan between the advertiser and Web host.
Ideas about the value of paid search have led to major discussions about PPC and other kinds of search engine marketing. Although it’s fair to approach the value of any search engine marketing plan on a case-by-case basis, experts have their own ideas about achievable ROI from PPC and how effective paid search is in general. Those who work in SEO and online advertising will often display the results of past campaigns to promote their arguments, but due to the very dynamic nature of the Web, it’s difficult to generalize about the effectiveness of any one type of online marketing strategy.