The LSU Code of Student Conduct defines plagiarism as the "[l]ack of appropriate citation, or the unacknowledged inclusion of someone else's words, structure, ideas, or data; failure to identify a source, or the submission of essentially the same work for two assignments without permission of the instructor(s)." (LSU Code of Student Conduct 10.1.H)
The University of Indiana has an excellent guide on Patterns of Plagiarism.