I will allow myself to be a bit pedantic here!
Non-English speaking people often confuse the verb "to devise" - (to contrive or invent), with the noun "a device," - (a piece of equipment, or a clever method). There is an easy trick to aid in remembering which is which: "devise" contains the verb "is," while "device" contains the noun "ice."
The term "devised," as popularly used now in theatre parlance, is actually a lazy contraction of "actor-devised." The verb "to devise" is a transitive verb, it needs an object to give it meaning, It just means "to figure (something) out," or "to concoct (something)." It came into use as a kind of defensive reaction. "Why isn't there a director listed in your programme?" We might have replied "Oh we're just a bunch of crazy anarchists. We're not into hierarchical structures!" But instead we just said "We actors did it ourselves." "Oh, you devised it yourselves?" "Yes, it's actor-devised."
The concept of devising is found within several art forms, and implies a method of collective creation of a work. As a word it is most associated with stage arts, where a group - actors, non-actors, yes even the public - with open and fluid leadership can struggle to produce a result that had not been pre-determined. It also implies a process in which the various elements of theatre are often not placed in an hierarchic or proscribed sequential order. The text may come last. Scenography can evolve alongside the actors' research into style or content. The essential elements of this open theatre form are both ancient (for example Commedia dell' Arte from sixteenth century Italy), popular (street theatre, role playing, student review) and can emerge at an internationally recognised professional level.
After many years of devising theatre, when I returned to working with a conventional text, it was so easy it felt like I was cheating!
There is nothing completely new or modern about actors devising theatre. It is very old stuff. Been around for millennia. Which is exactly why we at Footsbarn Theatre were interested in it. We wanted to go to the roots of theatre, back to before the intervention of the director. We were very insistent about this in the early days of the company so it is nice to see our pioneering work in what one might call "contemporary devising" briefly mentioned in Alison Oddey's influential book Devising Theatre (Routledge, 1994. Page 168)