Plagiarism is described in the W&L 2011-2012 Catalog, and cited by the Student Executive Committee, as "the use of another's words or ideas without proper ackowledgement."
The resources below should be considered reliable sources of advice about what constitutes plagiarism and how to avoid it.
Introduction, from W&L's Student Executive Committee.
Some faculty, such as Paul Gregory, also may have plagiarism advisory sites.
Comprehensive guide covers plagiarism, citation practices, collaborations, etc., originally created by current W&L Dean of the College Hank Dobin.
Guide from Northwestern University.
From Amherst College.
Excellent eight-page guide.
From Williams College.
Guide from Grinnell College.
From the College of William and Mary.
From Duke University.
From Georgetown University.
From the Writing Tutorial Services at Indiana University.
Brief guide from the University of Auckland (New Zealand).
Commercially-published guide to plagiarism and citations styles.
Focus on two sections of this site: the options ("Overview of Terms," etc.) in the column on the left; and the Self-Test (click on "Start the self-test"). From Colby, Bates, and Bowdoin Colleges.
There is a spcific section entitled "What Is Plagiarism?," but the entire site is helpful. University of Southern Mississippi.