Watch this video from WHMS Library to understand the difference between library databases and search engines.
In general, scholarly sources:
Articles published in scholarly journals which cover academic and scientific research. Scholarly journals are often referred to as "peer-reviewed" or "refereed" journals. Journals can also be scholarly or academic, but not have the extra level of quality control known as "peer review."
Books are not "peer-reviewed," like articles. Instead, they are written by academic scholars, and edited and published (most often) by academic or university presses, e.g.: Routledge, IGI Global, or Oregon State University Press.
A book review can also indicate if the book is scholarly. Use LibrarySearch to find reviews of books.
When in doubt, ask a librarian!
*LibrarySearch includes search results from many of the UO Libraries database subscriptions.
Databases often have a "Scholarly" or "Peer Review" filter option too. Here's an example from one of our EBSCO databases:
Search in LibrarySearch by title or keyword. Many of our books are "scholarly," but look for the name of the publisher to find an academic press, e.g., "Princeton University Press."