A subject-matter expert (SME) is a person who has accumulated great knowledge in a particular field or topic and this level of knowledge is demonstrated by the person's degree or licensure, i.e. a PhD in Chemistry could be easily declared as an SME in Chemistry, Even as a person with a Second Class Radio Telegraph License (or equivalent) issued by the National Licensing body (FCC in the United States, OFCOM in the UK, and NTC in the Philippines, and other authorities around the world) could be considered an SME in Radio Telegraph. A person with a Masters Degree in Electronic Engineering could be considered a Subject Matter Expert in Electronics.
The term is used when developing materials about a topic (a book, an examination, a manual, etc.), and expertise on the topic is needed by the personnel developing the material. For example, tests are often created by a team of psychometricians and a team of SMEs. The psychometricians understand how to engineer a test while the SMEs understand the actual content of the exam. Books, manuals, and technical documentation are developed by technical writers and instructional designers in conjunctions with SMEs. Technical communicators interview SMEs to extract information and convert it into a form suitable for the audience. SMEs are often required to sign off on the documents or training developed, checking it for technical accuracy. SMEs are also necessary for the development of training materials.