A layman or dilettante was a newcomer who possessed no accreditation in or advanced knowledge of a particular field.
In 2266, the android of Roger Korby asked whether James T. Kirk realized "the number of discoveries lost because of superstition, of ignorance, of a layman's inability to comprehend?" Kirk then posed "a simple layman's question" to "Korby" – where the other crewmembers who had landed on Exo III with him were now. (TOS: "What Are Little Girls Made Of?")
In 2369, Professor Galen referred to Jean-Luc Picard as a dilettante rather than a true scholar of archaeology. (TNG: "The Chase")
While cross-examining Doctor Julian Bashir that year, Ilon Tandro referred to himself as a layman in relation to the field of medicine. (DS9: "Dax")
In 2371, pleased by Kes' curiosity about anatomy and physiology, The Doctor gave her several medical texts to study, cautioning her that they weren't written for laymen. (VOY: "Eye of the Needle")
Later that year, he likewise cautioned Tuvok when the Vulcan asked for a copy of his neurological analysis of Tom Paris calling the report "virtually indecipherable" to the layman. (VOY: "Ex Post Facto")
In 2372, based on his home, Garak characterized Julian Bashir's character from the holoprogram Julian Bashir, Secret Agent as "some kind of rich dilettante with a fascination for women and weapons". Bashir denied it, saying his character was really a spy. (DS9: "Our Man Bashir")
In 2375, The Doctor defined nihiliphobia in layman's terms as "the fear of nothingness". (VOY: "Night")
Later that year, Torat called the term wormhole as a layman's term which described many phenomena, among them interspatial flexures. (VOY: "Counterpoint")