Applied Linguistics, as a general definition, is the scientific study of language. The aspects of language that this field studies include a myriad of dimensions that show how complex human language actually is.
Language is broken down into each of its linguistic components via the study of syntax, morphology, and grammar. Language is studied from the focus of meaning using semantics. The application of the parts of language into multiple and diverse uses is also a branch within applied linguistics that covers from scholarly works to artificial intelligence language.
The understanding of language as a phenomenology is studied in applied linguistics through the fields of linguistic anthropology, second language acquisition, and second language learning. The neural factors that enable humans to study language are studied through psycholinguistics. Evolutionary linguistics encompass the changes of language as humans and cultures evolve. Also under applied linguistics you have computational linguistics and forensic linguistics, with each analyzing the application of language within the fields of technology and the law, respectively.
All this being said, think about the many specialties involved in the study of language application. The applied linguist is every single person who tries to adapt "a" language system from its original location, on to another. It is also any type of professional who tries to analyze the function and use of language in different type of scenarios. Scholarly linguists, L2 teachers, and evolutionary researchers are classified as professionals of applied linguistics because they do explore the multiple use of each part of a language system onto a new situation.
Computer programmers definitely touch on computational linguistics as they make machines "read" encoded information as a new language. Legal workers who explore the names of laws, the disposition of legalities, and the use of specific terminology apply linguistics to the analysis of legal procedures. In all, an "applied linguist" is someone who knows that language is a complex, interactive, and changing system that no two people use in the exact same way.