What is the use of an index?

(If that's the question being asked...) Indexing in a database system or a simple file-oriented system is used to make different records easier to access quickly. An index would be used to find data based on a certain key value quickly by going directly to the first record with that key, instead of searching the entire database or file. Indices are also handy for linking one file to another, such as with related information in different tables in a relational database system.