Search Engine Marketing
SEM is a method of marketing using Search Engines which includes organic and paid results. Organic results are the free listings on search engines, while Paid Per Click (PPC) are the ads that often appear above and/or on a column to the right of the organic list.
Organic results are listed in the order of their relevance and authority, while PPC results are listed in the order of bid price and relevance. With PPC highest bid will move your ad up to the first page and may be listed first depending on relevance. To reach the first position in organic search often takes years of dedicated SEO work—depending on the search term and your competition.
The cost of PPC on Google has reached a point (often over $3 per click) and on competitive keyword phrases much higher, which has driven small businesses to look for other internet marketing methods (or at least to move over to Bing/Yahoo's PPC).
The longer the keyword phrase (longtail) the closer the customer is to buying. This is because the customer has already completed researching and has already narrowed down the purchase and is ready to buy. This means that using longer descriptive keyword phrases will bring less clicks, but a much higher conversion rate. Since you only pay for the number of clicks (not like banners that you pay per thousand views) longtail keyword phrases have to be researched to find niches that have results you can afford.