The word can be applied to any different mineral that takes the form of these very small crystals - druzy quartz is probably the most common, but you'll find calcite, dolomite, and dozens of others exhibiting druzy crystals.
Have you ever looked inside a geode and seen a fine, tiny sparkle all around the bases of the larger crystals, that looked like someone had spilled a bit of glitter, or like frost on a sunny morning? Those were the druzy crystals.
Druzy crystals are frequently used in jewelry, usually in the form of a pendant displaying these tiny crystals. Sometimes the less appealingly-colored specimens are dyed, or covered with a metallic vapor coating - if you find metallic-looking druzy jewelry, be aware that they are probably not naturally formed.