A mood board is a collage of visual elements like pictures, fabrics, and text used to convey a style or idea. Mood boards can be used when designing spaces by including colors, fabrics, textures, and styles. They have advantages of being quick to make, providing a visual design, and allowing evaluation of a design before implementation. However, disadvantages include the designer ignoring client requests, the client disliking the mood board, or it differing from the client's expectations.