Layman's terms

Plain English (or layman's terms) is a style of communication that uses easy to understand, plain language with an emphasis on clarity, brevity, and avoidance of overly complex vocabulary. It is commonly used in relation to official government or business communication. The goal is to write or speak in a way that is easily understood by the target audience. It is clear and straightforward, concise, free of clichés and needless technical jargon, and appropriate to the audience's developmental or educational level and their familiarity with the topic.

The term derives from the 16th-century idiom, "in plain English", meaning "in clear, straightforward language".

In 1946, writer George Orwell wrote an impassioned essay, "Politics and the English Language", criticising what he saw as the dangers of "ugly and inaccurate" contemporary written English – particularly in politics where pacification can be used to mean "...defenceless villages are bombarded from the air, the inhabitants driven out into the countryside, the cattle machine-gunned, the huts set on fire with incendiary bullets...". Two years later Sir Ernest Gowers, a distinguished civil servant, was asked by HM Treasury to provide a guide to officials on avoiding pompous and over-elaborate writing. He wrote, "writing is an instrument for conveying ideas from one mind to another; the writer's job is to make his reader apprehend his meaning readily and precisely."

Gowers' guide was published as a slim paperback Plain Words, a guide to the use of English in 1948, followed by a sequel The ABC of Plain Words in 1951 and, in 1954, a hardback book combining the best of both, The Complete Plain Words – which has never been out of print since. Gowers argued that legal English was a special case, saying that legal drafting:

...is a science, not an art; it lies in the province of mathematics rather than of literature, and its practice needs long apprenticeship. It is prudently left to a specialised legal branch of the Service. The only concern of the ordinary official is to learn to understand it, to act as interpreter of it to ordinary people, and to be careful not to let his own style of writing be tainted by it...

...
Wikipedia