Plagiarism, as defined in the 1995 Random House Compact Unabridged Dictionary, is the "use or close imitation of the language and thoughts of another author and the representation of them as one's own original work." Within academia, plagiarism by students, professors, or researchers is considered academic dishonesty or academic fraud and offenders are subject to academic censure, up to and including expulsion. In journalism, plagiarism is considered a breach of journalistic ethics, and reporters caught plagiarizing typically face disciplinary measures ranging from suspension to termination. Some individuals caught plagiarizing in academic or journalistic contexts claim that they plagiarized unintentionally, by failing to include quotations or give the appropriate citation. While plagiarism in scholarship and journalism has a centuries-old history, the development of the Internet, where articles appear as electronic text, has made the physical act of copying the work of others much easier, simply by copying and pasting text from one web page to another.

Plagiarism is not copyright infringement. While both terms may apply to a particular act, they are different transgressions. Copyright infringement is a violation of the rights of a copyright holder, when material protected by copyright is used without consent. On the other hand, plagiarism is concerned with the unearned increment to the plagiarizing author's reputation that is achieved through false claims of authorship.

Academia

In the academic world, plagiarism by students is a very serious offense that can result in punishments such as a failing grade on the particular assignment (typically at the high school level) or for the course (typically at the college or university level). For cases of repeated plagiarism, or for cases in which a student commits severe plagiarism (e.g., submitting a copied piece of writing as his or her own work), a student may be suspended or expelled. Many students feel pressured to complete papers well and quickly, and with the accessibility of new technology (the Internet) students can plagiarize by copying and pasting information from other sources. This is often easily detected by teachers, for several reasons. First, students' choice of sources are frequently unoriginal; instructors may receive the same passage copied from a popular source from several students. Second, it is often easy to tell whether a student used his or her own "voice." Third, students may choose sources which are inappropriate, off-topic, or contain incorrect information. Fourth, lecturers may insist that submitted work is first submitted to an online plagiarism detector.

In many universities, academic degrees or awards may be revoked as a penalty for plagiarism.

There is little academic research into the frequency of plagiarism in high schools. Much of the research investigated plagiarism at the post-secondary level. Of the forms of cheating (including plagiarism, inventing data, and cheating during an exam), students admit to plagiarism more than any other. However, this figure decreases considerably when students are asked about the frequency of "serious" plagiarism (such as copying most of an assignment or purchasing a complete paper from a website). Recent use of plagiarism detection software (see below) gives a more accurate picture of this activity's prevalence.