According to the Oxford English Dictionary, plagiarism is “the action or practice of taking someone else's work, idea, etc., and passing it off as one's own; literary theft” . In other words plagiarism can be characterized as academic theft. It is unethical and, in some cases, it is illegal. Plagiarism is a form of academic dishonesty.

Same words, no quotation marks 

In research writing, sources are cited to alert readers to the sources of your information and to give credit to the writers from whom you have borrowed words and ideas (INCORRECT)

The student has used the author's exact words, leaving out only a phrase, without quotation marks or a citation.

Incorrect paraphrase
In research writing, we cite sources for a couple reasons: to notify readers of our information sources and give credit to those from whom we have borrowed. (Hacker). (INCORRECT)

 The student has made only slight changes, substituting words such as "a couple" for "two", "notify" for "alert", and "our"/"we" for  "your"/"you," leaving out a few words, and giving an incomplete citation.

  A Solution (appropriate paraphrase)

  A researcher cites her sources to ensure her audience knows where she got her information, and to recognize and credit the         original work. (Hacker, 1995, p. 260). (CORRECT)

  This student has paraphrased in her own words, while accurately reflecting and citing the author's ideas.

  A Different Solution (quotation with cite)

  In her book A Writer's Reference, Diana Hacker notes, "In research writing, sources are cited for two reasons: to alert readers     the sources of your information and to give credit to the writers from whom you have borrowed words and ideas." (1995, p. 260).     (CORRECT)

  By introducing his source, the student signals that the following material is from that source. All verbatim words are in quotation   marks, and the source of the quote is cited with a page number.

There are three main forms of plagiarism:

1. Copying another person’s work, including the work of another student (with or without their consent), and claiming or pretending it is your own
2. Presenting arguments that use a blend  of your own and a significant percentage of copied words of the original author without acknowledging the source

Paraphrasing another person’s work, but not giving due acknowledgement to the original writer or organization publishing the writing, including Internet sites. The exceptions to this would be in relation to common knowledge

When using another person's words, to avoid plagiarism one must always do both of the following:

1. provide a citation, either in the text or in a footnote, and
2. either enclose their words inside quotation marks or put their words in a block of indented, single-spaced text.

It is no defense for the plagiarist to say "I forgot." or "It is only a rough draft." or "I did not know it was plagiarism."

In academic writing, if you copy or paraphrase another person's words, or adopt their ideas or data, without giving credit by citing the source, you are plagiarizing - whether you had intended to cheat or not. And universities do not take plagiarism lightly.

Applying, analyzing, criticizing or quoting other people’s work is perfectly reasonable and acceptable providing you always:  

• Directly quote another person's written or spoken words. Be sure to enclose these words and/or sentences in quotations marks!
• Paraphrase another person's spoken or written words. Paraphrase means to re-write in your own words; merely reordering or substituting words is still considered plagiarism!
• Use theories, ideas, opinions, research, etc. that are not your own.
• Use historical, statistical, or scientific facts or data that are not your own.

" In research writing, sources are cited for two reasons: to alert readers to the sources of your information and to give credit to the writers from whom you have borrowed words and ideas."

From: Hacker, Diana, A Writer's Reference, St. Martin's Press, 1995, p.260.