A concordance is a word list of all words used in a given work or by a given author ("whole-corpus"), alphabetically listed with context for each use of the word.  For instance, if you wished to know how often Shakespeare used the word "mad" or Marlowe used the word "magic," a concordance will tell you, and it will take you to each use in context. Concordances are immensely useful for thematic analysis of usage.  For most authors, try Mitsu Matsuoka's concordance site at Nagoya University (Japan) that covers nearly all our authors in the second half of the semester, plus rather a lot from 212.  Here's the URL--bookmark it against future need!: 

        If you do enough close-reading analysis, sooner or later you should want to see how and where your author used specific key vocabulary in other works.  He does not include Shakespeare's works, but the Open-Source Shakespeare Project hosts an excellent whole-corpus concordance at this URL:  A similar single-author concordance to the works of Chaucer is hosted by Gerard NeCastro at the University of Maine, Machias: