

Historically, an expert was referred to as a sage.

An expert can be believed, by virtue of credentials, training, education, profession, publication or experience, to have special knowledge of a subject beyond that of the average person, sufficient that others may officially rely upon the individual's opinion on that topic. Experts are called in for advice on their respective subject, but they do not always agree on the particulars of a field of study.

An expert, more generally, is a person with extensive knowledge or ability based on research, experience, or occupation and in a particular area of study. Best synonyms for 'subject matter expert' are 'domain expert', 'sme' and 'subject matter experts'. Informally, an expert is someone widely recognized as a reliable source of technique or skill whose faculty for judging or deciding rightly, justly, or wisely is accorded authority and status by peers or the public in a specific well-distinguished domain. An expert is somebody who has a broad and deep understanding and competence in terms of knowledge, skill and experience through practice and education in a particular field.
