A blueprint is a detailed technical drawing showing how something should be built or assembled. The term comes from an old reproduction process that produced blue backgrounds with white lines. Today, construction drawings are printed on white paper, but 'blueprint' remains common terminology for architectural and engineering plans. Blueprints show dimensions, materials, structural elements, and how different building systems (electrical, plumbing, mechanical) should be installed. They serve as the authoritative guide for construction, allowing contractors to build what architects and engineers designed. Municipal building departments review blueprints to ensure designs meet codes before issuing permits.