Low key is the commonly known slang term for restrained, moderate and controlled.
It is so widely spread, that it is one of the first slang terms in the English language, foreign speakers encounter first.
To know low key is essential, to keep an image of a disciplined person, when in fact you’re swinging between the two extremities.
The phrase has deep rooted musical origins, referring to a low pitch.
It has been used in this sense since at least the early 19th century, appearing even in Charles Dickens’ 1844 book “Martin Chuzzlewit”.
In the 1850’s low key was used to describe a voice tone, used in speech when spoken quietly, softly, in a whispering manner.
By the end of the century, it was already used in its more elaborate sense, in its current form.
By the 2000’s low key got so deeply embedded inside the English language, that it is often seen thrown around as an adverb, in the spoken language, as well as social media posts.
Hip hop had also embraced the expression, as several rap artists use the expression in their music.