A web index is an inventory or a kind of index of all information and documents that are accessible via the Internet. It makes it possible to search the Internet quickly. Without it, a search engine would have to completely search the web with its billions of pages for every query – that would cost far too much time. A web index is therefore the basis for search engines – but it is not the same as a search engine.
You can imagine a web index as a file in a library. With it one can find the suitable books to a special topic fast. In the Internet the Web index is a list of all web pages, pictures, videos, documents and other contents, which are accessible over the Internet.
Due to the high dynamics in the Internet the index must be constantly updated, so that it contains also newly provided web pages and content. The so-called web crawlers are responsible for this. These are programs that automatically “crawl” from website to website and index the contents of the pages visited.
Saving and updating such a large index is very time-consuming. Therefore you need either a very, very large computer centre or, and this is the plan of the osf, a network of many small ones who share the task.