Plagiarism is the ultimate form of academic dishonesty. It is trying to pass someone else's work and/or words off as your own.
Most students realize that they are not supposed to quote from another author's work without a citation. However, many students do not realize that paraphrasing an author without a citation is also plagiarism.
When in doubt, cite your source. It is better to look unoriginal than to look dishonest.
Citations not only locate a piece of writing within the context of a particular schoarly debate, they also allow writers to make claims based on the authority of another expert.