What IS "peer review" and why does it matter?
Peer review grows out of the 18th century Republic of Letters and the Royal Society, in which papers were submitted & reviewed by scholars before presentation and publication.
Now peer review is a process by which academic work is evaluated and improved before publication.
An article or book is submitted for review to an editor, who then sends it to 2 or 3 external reviewers, who in turn provide feedback and comments. They return the piece to the editor with notes, who then sends it back to the author. This process may repeat. This process improves the quality of a work, but also means publication takes Years after the work is written.
There is a different between "Scholarly" and "Peer Reviewed" sources.
Scholarly sources are a broad category of materials created by scholars and academics, and it includes peer reviewed material, but not all scholarly work is peer reviewed.
Examples of non-peer reviewed scholarly works:
These resources can be a great starting point and can direct you toward useful materials, but they are not peer reviewed.