The following information is taken from the Wikipedia.com description of vertical search engines:

Vertical search engines are not new. Websites that help users find people, shop, and get business information have existed for years. But the number of these search engines being introduced has greatly increased in recent years.

In fact, in the last three years, research analysts at Forrester Research, JupiterResearch, and MarketingSherpa have identified a new tier in search dubbed specialized search, which includes local, topical and vertical search. Local search is already a burgeoning subset, with Google Local and many newspapers offering this functionality.

Like consumers, businesses use the internet for a variety of needs. Sometimes they are looking for all the information they can get, and for that, the likes of Google and the Yahoo search engines are used. But more often they're looking for something very specific related to their businesses. That's where vertical search sites come in. Vertical search engines deliver to businesses what the big sites can't, without the use of complex keyword combinations: relevant and essential content versus an exhaustive return of information.

Advertisers on vertical sites are able to reach potential customers who are much closer to making a purchase decision than the average user on Google or Yahoo, according to Greg Sterling, an analyst with The Kelsey Group. He told Forbes.com that that's the whole motivation for advertising on vertical sites. For example, he said someone doing a search on Edmunds.com, an automobile search engine, is probably more serious about buying a car than someone doing a car search on a general search engine.

The cost of advertising on the large search engines is also likely to drive more marketers to vertical search. "Increasing competition and rising keyword prices should motivate search marketers to look for newer, viable opportunities to diversify their incoming traffic," said Sapna Satagopan, Research Associate at JupiterResearch.

"Vertical search is about to happen," says Gary Stein, Director of Strategy at Ammo Marketing, and a former Senior Analyst at JupiterMedia. "Market conditions are setting up for it: the popularity of search engines, the availability of tools to build it, and opportunities to make money. Advertisers are competing for keywords."

A study by JupiterResearch called, Vertical Search: Early Marketers Will Reap Rewards of Low Pricing, found that paid search is densely concentrated within primary categories, or verticals: retail, financial services, travel, and media and entertainment. These accounted for 79 percent of spending on paid search in the United States in 2004.