A web search engine is a set of software tools which combine to search for information on the Internet. Searching is actually the final activity undertaken by the system as first they must crawl the web for information and index that information. Most modern search engines return a series of pages (called the Search Engine Results Pages – SERPS). As the abilities of the crawling software used to gather this information have improved so has the variety of information returned. Google, for example, now includes image search results, social search results and maps as part of their standard SERPS.
Effective search engines were a big step forward from the human maintained web directories of the past. They allowed fresh and up to date content to be indexed and served to users much more quickly than it could have been checked and added to a directory. This does rely on a significant use of automated ranking and assessment of content which can be manipulated by specialist SEOs leading to a constant battle by the search engines to improve their systems and defeat these manipulations.