The definitions can change depending on your subject discipline. For a more detailed discussion, see the next page, titled "Long Answer."

But the short answer is that "Scholarly" generally refers to being written by scholars and for scholars, while "Peer Review" refers to a review and oversight process that certain scholarly sources go through before they get published.   

...In a subject-specific database like Communication & Mass Media Complete?

Most of the scholarly article databases we have on our Databases List include some way to filter for only articles published in peer-reviewed journals (A) or that are more loosely identified as "Academic Journals" (B). In Communication & Mass Media Complete, just scroll down from the initial search boxes to see the filters shown in the image below:

... In Google Scholar?

Unfortunately, Google Scholar does not offer any filters to limit your results to only peer-reviewed sources. Your only option (if you are not already familiar with the journal in question) is to look up the journal title in Google--or in a journal directory like Ulrich'sWeb to see if it uses peer review.

Hip tip: If you want to connect to Penn State's subscriptions to scholarly journals, especially if you are off-campus, use the Google Scholar link on the Libraries' Databases List. This will give you the "Get It! @ Penn State" links next to your results. Or, in your personal Google Scholar account, select Settings > Library Links and then make sure "Pennsylvania State University - Get It! @ Penn State" is selected. Get It! links make it easier to get through any paywalls by connecting you to our subscriptions (but the link itself is not necessarily an indicator of scholarly quality, just a retrieval convenience).  

Here's a tutorial about it:

... In the Libraries' collections?

 Just click "Advanced Search" in the FIND box on the University Libraries' site...

... and then make sure the box next to Limit to: "Peer reviewed publications" is checked: