What is search advertising and why does it matter?

According to Wikipedia, Internet search advertising is a method of placing online advertisements on Web pages. Search advertisements can be placed on Web pages that show results from search engine queries. Through the same search-engine advertising services, ads can also be placed on Web pages with other published content. Search advertisements are targeted to match key search terms (called keywords), entered on search engines. This targeting ability has contributed to the attractiveness of search advertising for ad buyers, since consumers often use a search engine to identify and compare purchasing options immediately before making a purchase decision. According to Piper Jaffray, global search ad spending is expected to grow to $44.5 billion by 2011.