Wiktionary
mood board
n. A collage created by a designer to convey a concept or theme.
Wikipedia
Mood board
A mood board is a type of collage consisting of images, text, and samples of objects in a composition. It can be based upon a set topic or can be any material chosen at random. A mood board can be used to give a general idea of a topic that you were given, or can be used to show how different something is from the modern day. They may be physical or digital, and can be "extremely effective" presentation tools.