A concordance is an alphabetical list or index of all the words in a book, or in a corpus of works, which often includes the citations where the word occurs in the text as well as the word's immediate context. Although e books often have "Search" features, which one might assume would make concordances irrelevant, the ease of use and sophistication of the search tools vary by e book provider. For these reasons, concordances are still useful.
General Concordances to Shakespeare's Works (Plays and Poems)
Concordances to Specific Plays