The disciplined reading of terroir, vintage and varietal in the glass, until your palate can name a wine's birthplace blind.
The word is French. In Middle French a sommelier was the court official in charge of moving supplies, and the name probably goes back to the driver of a pack animal. The examined craft, naming a wine by its taste and proving it before examiners, was born in Britain: the first Master of Wine examinations were held in 1953, and the first Master Sommelier examination followed in 1969. London is still where its examiners are based. The Institute of Masters of Wine works from there, and since that first exam only some five hundred people have earned the title. In Bermondsey, the Wine & Spirit Education Trust, founded in 1969, saw 134,000 candidates take its qualifications in 2023/24.
What you can realistically reach: A WSET Level 2 or 3 intensive (a few days to a couple of weeks) genuinely earns a recognised qualification and a structured tasting method. The Diploma, MW and MS titles are years beyond that — worth not confusing with a short course.
There is a real difference between a school that teaches you and a good-looking website, and too much of the internet is the second kind. Four instruments do the work, and every one of them is visible on the page you are already on.
If a place dodges these, that's your answer. It costs you nothing to ask, and it tells you everything.
This is the short version. The full method is here — the six questions, in order, for any craft anywhere.