Pop-in
When objects or textures snap into view instead of fading in, usually because they just crossed the draw distance or streamed in too late.
It has two common sources. One is LOD switches with no transition: a model jumps from a low to a high detail level and the change reads as a visible pop. The other is texture streaming — a surface first appears with a coarse mipmap and then sharpens once the full-resolution data has loaded from disk.
The countermeasures are to blend between detail levels (LOD cross-fade, often via dithered transparency), to prefetch content along the player's path, and virtualised geometry like Unreal's Nanite, which streams triangles finely enough that the switches rarely show. Foliage and shadows are the worst offenders.