DTG stands for Direct-to-Garment, and refers to a method for textile printing. Unlike other textile printing methods, such as heat transfer or dye sublimation, DTG printing process uses specialized ink in order to print directly onto the garment, using a DTG printer. The fabric fibers soak up the ink, and become part of the garment. This technology enables creating garment prints that do not crack, peel or distort in other ways.

Source: https://www.kornit.com/blog/glossary-item/dtg/