3D printing, also known as additive manufacturing, is a process that creates 3D objects by laying down successive layers of material based on a digital model. The document discusses how 3D printing works by using a 3D modeling program or scanner to create a virtual design, which is then sliced into layers and printed one layer at a time. Various 3D printing methods like fused deposition modeling, stereolithography, and selective laser sintering are described. Applications in construction mentioned include printed soil, emergency accommodation, and cool bricks. Advantages include higher productivity, lower costs, ability to manufacture complex structures, and less waste.