A moodboard is an inspiration board – a curated set of images, colours, typography and textures that establishes the aesthetic direction of a project before actual design work begins.
A moodboard is a conversation tool between designer and client: it lets you agree on mood and character ("premium and restrained" or "energetic and bold"?) without the cost of designing blind.
In the design process the moodboard appears early – after the brief, before first concepts. A well-built one contains not just pretty pictures but considered references: typography, photography, composition and details that will genuinely translate into the design.
Tip for clients: when reacting to a moodboard, talk about feelings ("this is too cold"), not solutions – solutions come later, in the design itself.