The word "plagiarism," from the Latin "plagiarius," meaning "kidnapper," is defined as the presentation of another person's words or ideas as your own. Whether intentional or accidental, plagiarism is a serious offense. Therefore, when conducting research, you should cite sources and also make it perfectly clear to what extent the sources were used. Moreover, you must cite not only direct quotes, but also any ideas you use, whether the sources are copyrighted or not.
Copyright laws protect the rights of people who create original works, and copyright infringement and plagiarism often overlap when others use large blocks of text from a source without the copyright owner's permission. However, according to Miguel Roig, Ph.D., "the use of relatively short quotes from a published work does not usually require permission from the copyright holder, as it typically falls under the 'fair use' provision," yet "extensive quoting of text from a copyrighted source can constitute copyright infringement" and this is true "even if a citation is provided according to established scholarly conventions."
The penalty for plagiarism is often severe. For example, if you are a student and accused of plagiarism, you will probably earn a zero for the assignment, but you could also receive an "F" in the course or possibly be expelled from college. Moreover, the charge of "academic dishonesty" will be a permanent part of your record and could prevent you from being accepted into another college. If you are a professional writer, the repercussions are just as serious, for if you're guilty of plagiarism, you could lose your job or even face a costly lawsuit for copyright infringement.
You do not have to cite a source if the information is considered common knowledge. For example, most Americans know George Washington was the first president of the United States and called the "Father of His Country." However, many Americans do not know Washington first gained public notice in 1753 when he carried a message of warning from the governor of Virginia to the French troops moving into the Ohio countryside.
In order to avoid charges of plagiarism, do not use large blocks of text from a written work; use only small portions. Moreover, even then, make certain you meticulously cite sources internally and provide full bibliographical information on the reference page. Also, remember that even when you're paraphrasing text (putting it into your own words), you still must cite the source because you are using the author's ideas.