Druse is a crystal-coated surface of rock, commonly used interchangeably but erroneously with vug.
but vugs are similar to geodes. actually geodes are a form of vug. but that is debate.

let's see a geode is a rough sphere like minerial that could be the size of ping pong to the size of a polar bear. it's lined with a thin layer of chaledony with a cavity that is filled with another minerial. the most commonly known is quartz, of course there are other minerials that could be found in it as well. Unlike a druse, a geode is separable by weathering as a discrete concretion from the minerial in which it occurs and its inner minerials are not of the same minerals as those of the enclosing minerial. druse are of the same minerials. also duses may contain water in them.