The word `index' is derived from the Latin word `indicare' meaning `to point out' or `to show'. An indexing periodical is an access tool to a systematically arranged list of periodical literature providing complete bibliographical references of already published individual items of primary documents, which a republished in regular interval. It is organised in a convenient manner to search the location of entries. An Index can be alphabetical, chronological, classified, geographical or numerical. They are access tools to identify and locate the required information which appeared in a particular periodical,
An `abstract' according to ALA Glossary (1983) is an abbreviated, accurate representation of a work, generally without added interpretation or criticism, accompanied by a bibliographical reference to the original work when appearing separately from it'. An abstracting periodical, in addition to having the above-mentioned features of an indexing periodical, gives the information content of the primary documents in a condensed form. Quite usually it functions like the surrogate of the original primary publication, like in the Chemical Abstracts.
In short, the major difference between indexing and abstracting services lies in the form and content. Indexing periodicals gives lists of articles with bibliographical details arranged in user-friendly order to enable a user to trace the needed information easily and quickly. Abstracting periodicals not only list the bibliographical details but also provide abstracts of documents in a specific field or a group of subject fields helping the reader for his choice of an article or a paper.