NDT-TKU is an improved 3D Normal Distributions Transform method for mobile robotic mapping proposed by Takeuchi from Nagoya University. It uses a two-stage converging process where the voxel size is adjusted based on point density during registration. This allows for higher accuracy while reducing computation compared to a single voxel size. The key aspects of NDT-TKU include overlapping voxels, trilinear interpolation, and dividing the registration into converging and adjustment states.