The short answer: A collection of information organized so that it is searchable and retrievable.
Academic databases (such as PubMed, Scopus, and Web of Science) collect information about journal articles, book chapters, conference proceedings, dissertations, and much more in a particular area of scholarship. This information is then made to be easily searchable by you, the user. Think of library databases as buckets and each bucket is filled with journal articles, conference abstracts, and other materials. Looking in multiple buckets offers more coverage. No single bucket will have all the information you need. Some databases also have subject-specific coverage, so your research question will also dictate the best databases to search.
Below are our most commonly searched databases and their subject areas: