Depending on your assignment, you may be asked to include a specific type of source, for example, an academic journal article. For the majority of your assignments you will be expected to use rigorous academic sources from peer-reviewed journals.
Academic sources (for example academic journals) are written by academics for academics, with an emphasis on theory, usually peer-reviewed (articles scrutinised by experts before being accepted for publication). Academic journals contain articles of a substantial length with references to further reading and research.
Example: The Lancet has goals that “are expressed in four domains of our work: medical research, clinical practice, global health, and news and comment. The journal’s editors will collaborate over any contribution that advances or illuminates medical science or practice, or that educates or engages readers on important matters in the practice, policy, and politics of research, medicine, and public health.” (Elsevier Limited, 2016)