An ultracrepidarian (from Latin ‘beyond the sole’) is someone who speaks or offers opinions on matters beyond their knowledge. They pretend to know more than they do to impress others.
The term draws from a famous comment purportedly made by Apelles, a famous Greek artist, to a shoemaker who presumed to criticise his painting. The Latin phrase “Sutor, ne ultra crepidam” (also, ”Ne ultra crepidam judicaret”), can be taken to mean that a shoemaker ought not to judge beyond his own soles. That is to say, critics should only comment on things they know something about.