put it simply, academic writing is writing that is used for school. Participating in a talk with other people is what it means, but this conversation is different from normal conversations. Yes, saying what you think is part of academic writing. But you have to say it in answer to someone or some group, and your thoughts have to be carefully expanded upon, well-supported, logically ordered, rigorously reasoned, and tightly connected.  There are different types of school writing. There are a lot of different reasons why we write in school. Reading responses, book reviews, argumentative essays, literature reviews, empirical research articles, grant proposals, commentaries, memoranda, and a lot of other types of writing are some of the things we write. Each of these types of academic writing is used for different things and has its own framework and language. When it comes to academic fields, academic writing is how information and ideas are created, shared, evaluated, improved, taught, and learned. Writing in an academic way is an important part of learning a subject and doing well in school. Controlling your academic writing gives you capital, power, and choice in how you learn, how you identify, how you practice your field, how you fit in socially, and how you move up in your job(Carroll, 2002:84) 
Language is not a set of rules or grammatical standards that you have to follow. Instead, it is a creative tool for making sense of things. Language gives writers a lot of grammatical choices that they can use to present information, build an argument, add points of view, include other people's ideas and voices, engage readers, narrow the focus, and organize discourse in a way that achieves their goals and meets the needs of their audience. Language is a big reason why people who don't speak English as their first language have trouble writing. 
Furthermore, not being familiar with the rules of academic writing, in addition to not having a deep understanding of the subjects being written about, is the main reason why many students and scholars have trouble writing for school. (Thaiss,2006:73)