Final answer:
An index is a feature in long documents used by readers to quickly find specific information by listing topics and their corresponding page numbers, usually found at the end of the document.
Step-by-step explanation:
In long documents, an index is used to assist readers in quickly finding information. This page feature lists keywords, topics, or names along with the page numbers where they can be found within the document. The index is usually found at the end of a book or document and is essential for navigating through extensive content efficiently.
The Bibliography, while useful, serves to provide references and sources used in the document rather than for quick information retrieval. A cover page provides basic information like the title and author but is not designed for navigating the document. Modern electronic versions of documents can include hyperlinks in bibliographies and tables of contents, enhancing navigation further. However, for non-electronic versions and swift access to specific content, the index is the most helpful.
Consider an example where a reader is looking for information on 'Photosynthesis' in a biology textbook. Instead of flipping through hundreds of pages, the reader can simply turn to the index, find 'Photosynthesis,' and be directed to the exact pages where the topic is discussed.