A unisex name is special because it can signify both a boys’ name and a girls’ name.
Of all common unisex names in the US, only about 2.8 % begin with the letter O… On the other hand, 1.8 % of common boys' names begin with the letter O, with only 1 % of girls' names. This means that the initial O is slightly more common in unisex names than in names that can be clearly assigned to a gender.
We classify names as unisex that are not just officially suitable for both boys and girls, but which have actually been used many times in the English-speaking world for both boys and girls in recent years. Some of the unisex names may have more female or male connotations for individuals, but this is often subjective and goes back to the fact that in your own circle of acquaintances, you might have a boy or man, or a girl or a woman, who has this name.