Secondary sex characteristic
A pair of ducks. The left one (with the brown head) is the female. It is slightly smaller, and camouflaged. The male on the right is easily noticed; his colouring and size are secondary sexual characteristics. They help him mate with females.
Secondary sex characteristics are features which make it possible to tell the sexes of a species apart. They are not directly linked to reproduction.
Male birds usually have much more colourful feathers (plumage), the females are usually better able to hide, because their plumage is camouflaged.
Well-known secondary sex characteristics in humans are the deeper voice, facial hair (beard) and more muscular build in men. Faces, generally, make a big impact. It is the part other people interact with.
However, the wider hips are needed to give birth. Babies are born through the space between the three bones of a woman's pelvis. So is doubtful to call this a secondary characteristic, except so far as the width helps attract mates.