A Chunk Error (or World Hole, Missing Hole, Beta Hole, Lag Pit or just Missing Chunk) is a somewhat common glitch in Minecraft which occurs when a chunk loads incorrectly. Chunk errors are most commonly client-side, meaning that the missing chunk is actually there, but the player just can't see it, but chunk errors can, in rare cases, be server-side, meaning the chunk actually is gone and that there is a hole in the world.
Chunk errors appear as 16 x 16 x 256 holes in the world, stretching from sky box to The Void. Chunk errors commonly occur while traveling by boat in an ocean, as you are traveling faster than walking, which gives chunks less time to load. On superflat worlds, Chunk Errors will appear as chunks of regular generated land.
However, chunks can still generate while walking across the world. Some chunk errors form beside each other, cutting of the rest of the map beyond that area. This typically happen when the server is not fully loaded. These types of chunk errors can be fixed by simply reloading the map or server.
Chunk Errors can be fixed by exiting the world and entering again, disconnecting and reconnecting/reloading the server. Normally only you will be able to see a specific chunk error, although it is possible for two or more players to see the same chunk error at the same time. It is possible to see other players in a chunk error, but they will appear floating in the air, acting normally.
Players can abuse chunk errors due to the fact that it is possible to see ores or dungeons in the side of a chunk error and then simply dig to them. If a player attempts to jump into a chunk error, the player will get stuck and will not be able to move, this can be fixed by exiting the world or server and joining again. Usually the chunk error will disappear after a period of time, but if it doesn't, jumping in is ill-advised, as it is most likely an actual hole.