Called a Web search, the process of looking for information online helps determine the usefulness of the Internet to particular users. The most common form of an Internet search takes place using a search engine to facilitate although many sites offer a specific type of in house search relevant to their niche such as a flight search though a site like www.webjet.com.au or www.flightsaustralia.com.au
Search engines evolved from the simple lists of Web servers that were popular in the early 1990s into the form that now is recognizable. Right now, most Internet users visit the most popular search engines, Google, Bing and Yahoo to perform a Web search. The results displayed are typically prioritized by relevance, so those who search the Web can quickly find material that is relevant to their needs. Without a search engine, finding information and resources on the Internet is very difficult, especially when specific servers and domains containing desired information are unknown.
The reason a search engine helps people search for information online is because they regularly crawl the Internet looking for servers and indexing the information they contain. As long as Web hosts are discoverable to the search engine crawlers, the information they contain will at some point be included in the index.
Because different search engines use different algorithms or methods to crawl Internet hosts, they often display different results. Making a thorough search of the Web may therefore require multiple searches using different search engines. To help automate the process of searching multiple sites, users can use meta-search engines which combine the search results from multiple search engines into a single comprehensive list. Although the meta-search engine concept has never caught on as a mainstream way to search the Web, it does offer new ways to make faster and smarter online searches.
Hosts that are not discoverable on the Internet using a variety of techniques comprise the so-called invisible Web. These are Web hosts that either block search engines from crawling them or they are hosts that use non-ICANN domains. Although some efforts to facilitate Web search on the invisible Web exist, finding information among those alternative sites is still difficult for most people. Many Internet experts suggest that a large portion of the Internet is inaccessible by search engine users, meaning that a vast amount of information located on the Internet is inaccessible to most people.