The Triplanar projection works in conjunction with a Triplanar map. It takes the coordinates in world or object space and picks the projection axis based on theTriplanar map node's active axis. This gives a quick way to map a Texture on any object, and presents the possibility for texture transforms local to each projection axis. The Triplanar map node has six input pins representing the positive and negative X, Y, and Z planes. You can map the same or different Texture nodes to each of these input pins.
Figure 1 shows the Triplanar projection connected to each Texture node applied to a Triplanar map node.
Figure 1: The Triplanar projection connected to Texture maps feeding into a Triplanar map node