Plagiarism is "an act of copying the ideas or words of another person without giving credit to that person" ("Plagiarism"). This can mean:
Essentially, plagiarism is taking the work of someone else, and making it seem as though it is your own original idea, thought, words, or work.
You can avoid plagiarism by giving credit to the original creator, just like I did here! Above, I quoted the Merriam-Webster dictionary's definition of plagiarism - I used their exact words. So, to give them credit, I included a citation and a reference below. By including this information, I let you know that these were not my words, and also told you where I had gotten them.
Here are a few examples of plagiarism that made the news. Follow the links to read more about each of these cases.