CDLOD
A terrain scheme that morphs a heightmap's vertices between levels of detail in the vertex shader, so LOD transitions become invisible.
CDLOD (Continuous Distance-Dependent Level of Detail) was described by Filip Strugar in 2010. A heightmap is split into a quadtree of tiles; the distance to the camera decides which level each tile is drawn at. The novelty is that the transition is continuous — near a level boundary, the vertex shader interpolates each vertex toward its coarse-level position.
This avoids "popping", the jarring jump that happens when a terrain tile suddenly changes resolution. Compared with older methods like geomipmapping and chunked LOD, CDLOD moves the morphing onto the GPU and keeps CPU work minimal, which suits large open worlds.