“Academic writing refers to a style of expression that researchers use to define the intellectual boundaries of their disciplines and their specific areas of expertise. Characteristics of academic writing include a formal tone, use of the third-person rather than first-person perspective (usually), a clear focus on the research problem under investigation, and precise word choice. Like specialist languages adopted in other professions, such as, law or medicine, academic writing is designed to convey agreed meaning about complex ideas or concepts for a group of scholarly experts.” (Academic Writing. Writing Center. Colorado Technical College; Hartley, James. Academic Writing and Publishing: A Practical Guide. New York: Routledge, 2008.)

“Academic writing and publishing is conducted in several sets of forms and genres.[ . . . ] Writing in these forms or styles is usually written in an impersonal and dispassionate tone, targeted for a critical and informed audience, based on closely investigated knowledge, and intended to reinforce or challenge concepts or arguments. It usually circulates within the academic world ('the academy'), but the academic writer may also find an audience outside via journalism, speeches, pamphlets, etc. Typically, scholarly writing has an objective stance, clearly states the significance of the topic, and is organized with adequate detail so that other scholars may try to replicate the results. Strong papers are not overly general and correctly utilize formal academic rhetoric. While academic writing consists of a number of text types and genres, what they have in common, the conventions that academic writers traditionally follow, has been a subject of debate.” (https://sites.middlebury.edu/middsciwriting/overview/)

“A broad definition of academic writing is any writing done to fulfill a requirement of a college or university. Academic writing is also used for publications that are read by teacher and researchers or presented at conferences. A very broad definition of academic writing could include any writing assignment given in an academic setting.” Here is a list of documents where academic writing is used. Some are self-explanatory and some have a brief explanation.

Books and book reports

     Translations
     Essays
     Research paper or research article
     Conference paper
     Academic journal
     Dissertation and Thesis - These are written to obtain an advanced degree at a college or
     university.
     Abstract - This is a short summary of a long document.
     Explication - This is a work which explains part of a particular work.

http://grammar.yourdictionary.com/word-definitions/definition-of-academic-writing.html

Everything you need to know about academic writing in a nutshell, you will find here: https://learn.solent.ac.uk/course/view.php?id=31631&section=0