Scholarly Sources are those that have gone through the process of being reviewed by other established scholars in that field.
Professional Sources are those that are written by professionals in a field but have not been reviewed by other professionals in the field.
A way to be absolutely sure an article is from a peer-reviewed journal is to look in the database, UlrichsWeb (see link below). When you find your journal in UlrichsWeb, make sure there is a referee jersey icon associated with the title.
Check out these databases if you are looking for scholarly articles.
Below are some databases that will be more relevant/useful for "social work." Be sure to "scroll" down through the box to see additional choices.