A blueprint is any exact or detailed plan or outline of a product, program, project or vision; it is detailed plan of action; a model or prototype; a detailed operational plan for undertaking a project.
Literally, a blueprint is a two-dimensional set of drawings that provides a detailed visual representation of how an architect wants a building to look. Blueprints typically specify a building's dimensions, construction materials, and the exact placement of all its components.
Blueprints are generally recognizable from their blue background and light-colored lines. To that end, a blueprint can be defined as a photographic print made with white lines on a blue background.
In essence, a blueprint is a documented image that shows how something will be made.