The University of Maine defines plagiarism as "...the stealing of words, ideas, images, or creative works." This is basically taking somebody else's idea, verbatim, and presenting it as your own. This is a federal crime.
If you were writing a paper about skiing and you used the phrase "skiing is an ancient ritual that has been around for centuries" by copying it directly from another source, this is plagiarism. However, using common knowledge is not considered plagiarism. If you write that Neil Armstrong was the first man on the moon, you are not committing plagiarism. It only becomes plagiarism when you take somebody else's original and creative idea and present it as your own.
There are many reasons people plagiarize. Sometimes, when they are in school, they are in a big rush to finish a paper or story that they didn't take the proper time to write. Out of desperation, they will use somebody else's work just to get done. Some people plagiarize to make themselves look better than their talents.
Sadly, plagiarism has become a major concern at many U.S. universities. The University of Florida quotes some disturbing statistics. They report that "66 percent of 16,000 students from 31 prestigious U.S. universities have cheated at least once..." and that 12 percent of those people considered themselves as cheating regularly. This means that 10,560 of those 16,000 have committed plagiarism at least once and that 1,280 of those cheat regularly. The University of Florida quotes a study by Who's Who Among American High School Students that states that "four out of five high achievers" in a 1998 survey admitted to cheating. Half of those students believed cheating wasn't a big deal. Few of them got caught. Perhaps the most disturbing statistic the University of Florida reports comes from the University of California-Berkley, where plagiarism increased by 744 percent in the years between 1993 and 1997.
If you plagiarize on a college paper and are discovered, you will immediately fail the course. The university also has the right to kick you out of the program and, if they like, pursue legal action. Plagiarism is generally considered a misdemeanor. Muhlenberg College reports that most plagiarism fines are between $100 and $50,000 dollars with up to one year of jail possible. They also report that plagiarism is considered a felony if the plagiarist earns more than $2,500 dollars from their plagiarism. In this case, fines may be up to $250,000 and ten years of jail time is possible.
Sometimes, people plagiarize accidentally because of simple ignorance. Although this is no excuse, it can be understandable that some people simply didn't understand how to avoid plagiarism. Avoiding plagiarism is actually incredibly easy. If you are writing a paper for a class and you want to use a direct quote, simply attribute it to the source. This can be as simple as writing "George Miner wrote that..." before the quote. Doing this before every quote you give will guarantee you will not be plagiarizing. Giving yourself enough time to finish any assignment and taking the time to craft your own ideas will also avoid any chances of plagiarism.