This term stands for what is produced when you enter a keyword into a search engine such as Google.
Results will often include searches known as natural search, paid search (Keyword Advertising) and results based on manual insertion.
Most users are going to look at the top three natural search results first, and therefore working to get your site at the top of natural search listings is far more important than buying keywords, however, the competition may be so great that buying keywords is necessary to get the traffic you want.
In the case of Google, you can purchase keywords through their AdWords program. Each time someone clicks on the keyword, you pay Google for that click. If no clicks happen, you won't pay for your keywords and link being displayed.
Users will benefit from putting more than just one word in the search box on any search engine. Focus on entering specific words key to the results that you are requesting. This will narrow the results given back, and save you considerable time searching for the information that you are seeking.
Many search engines offer you several different ways that data can be returned to you narrowing the content. Specific searches include but are not limited to local searches, images, videos, maps, news, ecommerce, blogs, finance, weather and more. Again, use all the tools you can to narrow what you are looking for and you will often get a superior result.