Stereolithography (SLA) is an additive manufacturing process using a vat of liquid UV-curable photo polymer and a UV laser to build your parts one layer at a time. On each layer, the laser beam traces a part cross-section pattern on the surface of the liquid resin. Exposure to the UV laser light cures, or, solidifies the pattern traced on the resin and adheres it to the layer below. Layer by layer your 3D data becomes a solid part. 
This is the most common rapid prototype process that yields a semi strong part with very good accuracy.

selective laser sintering.

Selective Laser Sintering (SLS)is an additive manufacturing process that uses a high power CO2 laser to fuse small particles of plastic, metal, ceramic, or glass powders into a mass representing a desired 3-dimensional object. The laser selectively fuses powdered material by scanning cross-sections generated from 3-D data of the part on
the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness,a new layer of material is applied on top with a roller, and the process is repeated until the part is completed.  See illustration below.

3D PRINTER

A liquid bonding agent selectively deposited to join powder. You can print multiple metal parts at once in various materials.