A specialised or modified leaf, mostly associated with the reproductive part of the plant, such as the flowers, inflorescence, or cone.
They often have an attractive or protective function, and mostly differ from the actual leaves of the plant—in shape, colour, and size. On a pineapple, they're the spiny, rough bits you feel on the rind, just underneath each of the single parts that make up the fruit. On a conifer cone (pine cones, fir cones, giant sequoia cone) a layer of them separates each row of scales from one other, in most cones the bracts are smaller than the scales and you can only see them when you start taking apart the cone. On some cones the bracts extend beyond the scales, and they overhang on each scale.