Academic language is the specialized words and style that scholars in an academic field use to communicate formally with one another in articles, books and reports. Academic language is often very difficult to understand when you first read it. Each academic field has its peculiar ways and you have to read the language carefully.
Everyone has a hard time understanding what is going on when they read scholarly research for the first few times. It takes a lot of experience to become comfortable with reading academic language-- and even more experience writing a paper in academic language. It is a craft.
Compare an article from the New York Times about learning and self-deception -- written so that most people with some high school education can understand it -- to that of an abstract of a scholarly article on the same topic written in academic language from one of the experts mentioned in the article. You can see that academic language is very precise, concise and very cautious. Ideas are stated in as few words as possible. There is little repetition or restatement of ideas to make it easier to comprehend. The reputations of the authors are at stake and other scholars expect certain things to be said in certain ways. The writers will assume you know a lot about what they are discussing to begin with, and use vocabulary that may sometimes look familiar but has a meaning that is very specialized to the academic field.
The topics of academic language also tend to be very, very specific and make very narrow claims about what the research being described actually means. Don't expect to find a scholarly article that gives you a general overview of a topic and sweeping statements that clearly state what the larger signifigance of what is being written about.
Based on discussion in Snow, Catherine E. Academic Language and the Challenge of Reading for Learning About Science. Science 23 April 2010: Vol. 328 no. 5977 pp. 450-452 DOI: 10.1126/science.1182597