Subject-matter expert
A subject-matter expert (SME) is a person who has accumulated great expertise in a particular field or topic, which expertise is reflected by the person's degree, licensure, and/or years' occupational experience in the subject. For example, a PhD in chemistry may easily qualify as an SME in chemistry, a person with a Second Class Radiotelegraph License or equivalent issued by the national licensing body is an SME in radiotelegraphy, a person with a master's degree in electronic engineering is an SME in electronics, and a person with many years' experience in machining is an SME in that field.