What are scholarly sources?
Scholarly sources are a type of information source, such as books or journal articles, that go through a rigorous review process. Sometimes you will hear scholarly sources called academic sources or peer-reviewed sources. When a researcher decides to publish in a scholarly source, her research is reviewed by 2-3 other subject experts. These experts help determine if the research is high-quality and ready to be published. This process is called peer-review, and while it is not always perfect, it is a widely accepted standard in academia.
Scholarly sources are contrasted with popular sources. To see the differences between these two types of sources, see the Scholarly v. Popular Infographic.
What are journal articles?
Researchers in many disciplines publish in scholarly journals. These publications typically come out multiple times a year - kind of like magazines. Most of the time, journals have a very specific focus. For example, the journal Cultural Anthropology is a peer-reviewed journal that publishes ethnographic research. When you search most of the library's resources, you find electronic versions of articles that were published in journals.