Concept

A concept or concept art is a piece of art that defines and explains an idea. For VFX we sometimes get concepts that we then try to implement in the game. The concept should describe the feel, coloration and movement of the effect. It should also be tied to the lore of the game so it fits the gameworld. The reason concept is used is because it's faster to iterate on than an actual implementation of the effect.

https://conceptartempire.com/what-is-concept-artist/