Key Word in Context
KWIC is an acronym for Key Word In Context, the most common format for concordance lines. The term KWIC was first coined by Hans Peter Luhn. The system was based on a concept called keyword in titles which was first proposed for Manchester libraries in 1864 by Andrea Crestadoro.
A KWIC index is formed by sorting and aligning the words within an article title to allow each word (except the stop words) in titles to be searchable alphabetically in the index. It was a useful indexing method for technical manuals before computerized full text search became common.
For example, the title statement of this article and the Wikipedia slogan would appear as follows in a KWIC index. A KWIC index usually uses a wide layout to allow the display of maximum 'in context' information (not shown in the following example).
|KWIC is an||acronym for Key Word In Context, ...||page 1|
|... Key Word In Context, the most||common format for concordance lines.||page 1|
|... the most common format for||concordance lines.||page 1|
|... is an acronym for Key Word In||Context, the most common format ...||page 1|
|Wikipedia, The Free||Encyclopedia||page 0|
|... In Context, the most common||format for concordance lines.||page 1|
|Wikipedia, The||Free Encyclopedia||page 0|
|KWIC is an acronym for||Key Word In Context, the most ...||page 1|
|KWIC is an acronym for Key Word ...||page 1|
|... common format for concordance||lines.||page 1|
|... for Key Word In Context, the||most common format for concordance ...||page 1|
|Wikipedia, The Free Encyclopedia||page 0|
|KWIC is an acronym for Key||Word In Context, the most common ...||page 1|
The term permuted index is another name for a KWIC index, referring to the fact that it indexes all cyclic permutations of the headings. Books composed of many short sections with their own descriptive headings, most notably collections of manual pages, often ended with a permuted index section, allowing the reader to easily find a section by any word from its heading. This practice is no longer common.
References in Literature 
Note: The first reference does not show the KWIC index unless you pay to view the paper. The second reference does not even list the paper at all.
- David L. Parnas uses a KWIC Index as an example on how to perform modular design in his paper On the Criteria To Be Used in Decomposing Systems into Modules, available as an ACM Classic Paper
- Christopher D. Manning and Hinrich Schütze describe a KWIC index and computer concordancing in section 1.4.5 of their book Foundations of Statistical Natural Language Processing
- Manning, C. D., Schütze, H.: "Foundations of Statistical Natural Language Processing", p.35. The MIT Press, 1999
- Advanced Indexing and Abstracting Practices.