pla·gia·rismnoun \ˈplā-jə-ˌri-zəm also -jē-ə-\: the act of using another person's words or ideas without giving credit to that person : the act of plagiarizing something.
Example of a citation: Source: "Plagiarism." Merriam-Webster.com. Merriam-Webster, n.d. Web. 16 Sept. 2014. <http://www.merriam-webster.com/dictionary/plagiarism>
To avoid plagiarism it is important you practice documenting, sourcing, and citing the information you find to support your research. You must give credit to the authors of the information you use by creating a bibliography or a works cited page. In addition, when you reference these authors you must use quotes, if you are using the author's exact words. Practice in-text citing and paraphrasing to note when and where you're including the author's ideas and/or restating the information in your own words.
Note: Purdue Owl Writing Lab provided below is a great resource for practicing these skills.
The use of images, pictures, photos, clip art , etc. is another way students often plagiarize. It's easy to do, because you perform a search and the images are simply generated. Most students click on the images tab, scroll or scan through the results and select the image they feel best represents what they're looking for. In general and at the very least, you should provide the location or website of the image. You should provide a caption describing the image, as well as, where it originated in parenthesis. In the best case scenario, you should provide a citation in your works cited or bibliography page. Most importantly, these images must be appropriate to use and you should make some attempt at determining whether the image is protected or not. TIP: If the statement or words you include in your writing are highly descriptive and expert-like and the content is known to be foreign by design (meaning that it wasn't anything you already knew) then it could be an indicator to your teacher that you COPIED it. There is no problem in using the word or word(s), just as long as you let the teacher know who and where you got it from. Use the appropriate format to receive full credit.
The following web resources can be used to properly document, source, and cite information for your bibliography or works cited page.
Note: Your English teachers do have access to a versioin of TURN IT IN as a companion to one of your textbooks. This means that your teacher could check your work (e.g. Essay) and if it is found in this source you may be penalized for cheating or being dishonest.