Advanced search refining options differ from one search engine to another, but some of the possibilities include the ability to search on more than one word, like searching leak detectors, to give more weight to one search term than you give to another, and to exclude words that might be likely to muddy the results. You might also be able to search on proper names, on phrases, and on words that are found within a certain proximity to other search terms.
Most search engines use search term frequency as a primary way of determining whether a document is relevant. If you're researching leak detectors and the words appears multiple times in a Web document, it's reasonable to assume that the document will contain useful information. Therefore, a document that repeats your words over and over is likely to turn up near the top of your list.
