First, remember there is a difference between a reputable source and a scholarly one. As social workers, you will use many, many sources that are reliable but not scholarly. Demographic data, government reports, policy briefs, news reports, professional white papers, etc. are all reputable, appropriate sources but aren’t scholarly. Remember to check with your instructors on how much non-scholarly work you should use. Also remember this is assignment-specific: a research paper on a policy will have more non-scholarly references than will a paper exploring a research question.
Secondly, not all scholarly sources are peer-reviewed. Peer-review refers to a specific process that only some (granted most) academic journals use. Dissertations, academic books, and encyclopedias are scholarly, but not peer-reviewed.
(Note that Wikipedia, therapy.org, or general purpose online dictionaries are never appropriate. Use scholarly encyclopedias for overviews and definitions.
Lastly, there isn’t one specific definition of a scholarly source because it’s so discipline specific. In general, scholarly works are written by a scholar (that is, someone with an academic degree in that subject area), and are intended to be read by scholars. In other words, if it’s intended for the general public, it probably isn’t scholarly.