There a many types of processes depending on the material printed or the technique used by the company making the printer.
The molten plastic deposition type is one method, however there is also a type where thin layers resin are spayed/deposited in ultra thin layers and cured by ultra violet light, another method laser sinters powdered nylon and variations on this can fuse powdered metals too, and another type mentioned binds plaster powder together.
More technologies out there, and many are in development. There's a major push to improve print times, which will of course lower costs.