Professors use a lot of different phrases to describe a specific set of publications. Whether they call it Academic or Scholarly, what they frequently mean is that they want you to find articles by researchers that have been published in a peer-reviewed journal. These articles are mainly written by people who work or teach (and thus are considered "scholars") in their respective fields and contain original research on very specific topics within their field.
In addition to the research-based articles published in peer-reviewed journals, there is a lot of work that is published by scholars in other types of publications. Professionals might present at a conference and have their presentation written up in conference proceedings, write a chapter in a book on a topic that is edited and collected by other scholars, or even write an editorial for the publication they edit. While these are not always based on original research or peer-reviewed they are typically outstanding sources.