The peer review process is done at the article level, and then published in an issue of a journal. Just like with a popular magazine, lots of different types of content goes into a journal - not just peer reviewed articles. When you find a potential article, make sure you double-check that it's not one of those other types of content (editorial, book review, column, opinion piece, etc).
Depending on the field, assignment and professor, you may be asked to find peer reviewed, refereed, academic, or scholarly articles. If you're confused about assignment requirements, we strongly encourage you to discuss them with your professor!
These terms are interchangeable with each other - the articles are always either reviewed or refereed by multiple experts (peers) in a highly structured and critical process. The author then receives that feedback, makes changes and resubmits the work, and then the journal editor decides whether or not to publish it.
These terms are interchangeable with each other, and these articles are not always peer reviewed/refereed. These articles are still research focused and heavily sources (lots of references), and written for an academic audience, but they may have only been reviewed by an editorial board, rather than content experts.
According to Understanding Science, peer review does the same thing for science (and other fields of study) as the "inspected by #7" sticker does for your t-shirt: provides assurance that someone who knows what they're doing has double-checked it. The peer review process typical works something like this:
This video from the NCSU Libraries quickly and concisely discusses how articles get peer reviewed, and the role of peer review in scholarly research and publication.