Relevancy refers to the appropriateness of the source for your needs.
Ask yourself these questions when thinking about if a source is relevant or not:
For example, if you are required to use primary documents in a research paper about colonial America, it's important to find primary documents about colonial America as opposed to secondary documents about World War II.
For example, if you want to find general information about your favorite reality TV star, you don't have to worry so much about the type of source you use or the scope of the information.
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(Thank you to Tacoma Community College https://tacomacc.libguides.com/c.php?g=373171&p=2523161)