Gaudy means showy in a way that's too bright, too decorated, or overdone. Something gaudy tries so hard to be impressive that it ends up looking cheap or tacky instead. A gaudy necklace might be covered in huge fake diamonds and glittery gold paint. A gaudy costume might have so many sparkles, feathers, and clashing colors that it hurts to look at.

The word carries a negative judgment: it suggests bad taste. A room decorated with too many clashing patterns, oversized furniture covered in gold leaf, and neon lights everywhere would be gaudy. The problem isn't that these things are colorful or decorative; it's that they're excessive and poorly combined.

Sometimes people confuse gaudy with simply fancy or elaborate, but there's an important difference. A fancy ballroom with crystal chandeliers and elegant decorations isn't gaudy if everything works together tastefully. Something becomes gaudy when it crosses the line from “impressively decorated” to “overwhelming and tacky.” Think of the difference between a beautifully wrapped present with ribbon and gold paper versus one covered in twelve different ribbons, glitter glue, stickers, and aluminum foil all at once.