To plagiarize means to:
Steal and pass off (the ideas or words of another) as one's own;
Use (another's production) without crediting the source;
Commit literary theft;
Present as new and original an idea or product derived from an existing source.
(Merriam-Webster Online Dictionary definition of "plagiarize," retrieved June 20, 2017)
The following definition of plagiarism is excerpted from the California State University Northridge Catalog, 2019-2020.
Intentionally or knowingly representing the words, ideas or work of another as one’s own in any academic exercise. Comments:
Materials that contribute only to one’s general understanding of the subject may be acknowledged in the bibliography and need not be immediately footnoted. One footnote is usually sufficient to acknowledge indebtedness when a number of connected sentences in the paper draw their special information from one source. When direct quotations are used, however, quotation marks must be inserted and prompt acknowledgment is required.
Obtaining copyright permission is necessary if you wish to legally use another person's original works of authorship, including literary, dramatic, musical, artistic (includes images and photographs), and certain other intellectual works. Find out more about how copyright works at Permission: What is it and why do I need it?
Also, see the Library's Copyright & Intellectual Property Library Guide for more information about copyright.