SLA was the first 3D-printing technology. In 1986 Charles W. Hull developed the technology in his garage and later founded 3D Systems, the biggest company for 3D-printing machines to date.
VPP is the general term for 3d printing from a liquid phase feedstock material. A light hardening polymer is used, a laser or light projector is scanning or projecting the shape of the 2-dimensional slice on the top or bottom of the liquid, where it then hardens. After that a layer of liquid is brought between the hardened layer and the light source. Then the procedure is repeated until the part is done. After cleaning the part from the liquid it usually has to be cured in a UV-oven.