Basically KB stands for kilobyte, what that means is the larger a gif or file is, the more kilobytes it has. If it's really big, it could have MB or GB (megabytes and gigabytes). If a gif only has like let's say 10 frames, the KB size will be small. If it's over 100 or 200, it'll be huuuge and probably would end up being a megabyte.