Applied linguistics is the study of language in relation to practical problems. It originated in language education but now applies to other fields like speech therapy and translation. According to the document, applied linguistics aims to investigate language problems and find practical solutions. It draws from various disciplines like linguistics, psychology, and sociology. Applied linguistics covers areas like second language teaching and learning, as well as language disorders, therapy, and professional language uses. The overall goal is to better understand language's role in human affairs and provide knowledge to make language-related decisions.