According to Merriam-Webster, to plagiarize is "to steal and pass off (the ideas or words of another) as one's own : use (another's production) without crediting the source."
This is why it is important to always cite your sources, whether it's a direct quote you are using or someone else's idea. To lean more about plagiarism, check out plagiarism.org.
Sites that explain what plagiarism is and how to avoid it.
These are a few articles that discuss the issue of plagiarism at the college level.
If you are worried that you missed something, you can use a plagiarism checker for help. There are tons of options, but below are some of the free options out there. Of course, as with all things free, these sites have a few limitations.
The University of New Orleans policy on plagiarism is defined within the Academic Dishonesty Policy. For an explanation of the policy please find at the link below:
Et Plagieringseventyr (A Plagiarism Carol)
This video illustrating the pitfalls of plagiarism, is brought to you by the University of Bergen.