Spiky means covered with sharp, pointed projections that stick out. A cactus is spiky, with needles that can prick your finger if you touch them. A porcupine has spiky quills covering its back for protection. Hedgehogs have spiky spines that stand up when they're frightened.

The word describes anything with lots of pointy bits jutting out in different directions. A punk rocker might style their hair into spiky peaks using gel. Even a graph showing inconsistent data might be called spiky because its line jumps up and down sharply instead of flowing smoothly.

People sometimes describe personalities as spiky too. A spiky person might be prickly or defensive, difficult to approach without getting a sharp response, like the way you'd hesitate before touching a cactus. But this usage is less common than the literal meaning of having actual sharp points.

The sensation of touching something spiky is unmistakable: your skin meets those points and immediately warns you to pull back. That's exactly what makes spikiness useful as a defense, whether you're a plant protecting itself or a teenager protecting your personal space with an intimidating hairstyle.