Tropical Freeze Textures: the TXTR format. RTB and Parax pretty much figured it out.

[Parax]

Right, did some digging around to refresh my memory - I think depth is the correct name for that variable. It's a 3D texture where the depth value is part of the texture dimensions (width = X, height = Y, depth = Z). Function definition of GX2InitTexture basically confirms it; it takes a u32 parameter "depth" right after width/height.