Scope is a general term which refers to what is covered in the source. It tends to be descriptive. Does the content only cover general information on a topic or does it provide great detail on a specific subtopic? How is the information presented? What is included and what is not?
Suppose you are looking for a source about a disease. You find two sources. The first source provides a descriptive narrative by someone who has the disease. They are not a doctor or healthcare provider. They discuss what it is like to have the disease to the best of their understanding. They talk about how they feel. They talk about what the treatment experiences are like. The second source lists the cause, the symptoms, the diagnosis, the treatment options, and the prognosis (likely outcomes) of the disease. It uses very technical language used by healthcare providers. It includes great detail about treatment options using complicated language.
Both sources provide information but may not necessarily be appropriate for your project or assignment. The first may more accurately depict the experience of having the disease for non-scientists. The second provides more objective, clinical information for the healthcare professional.
Be careful, however, that you do not discard a source because it does not include EVERYTHING you wish to know. Research often involves putting together a puzzle--finding a little information here and a little more there--to build an accurate picture of your topic. Sometimes students ignore good sources because they are searching for the perfect source which already says everything they wish to say. If everything had already been collated and written, there would be no need for research!