More generally, a soprano is the highest member of a group of similar instruments (for example, the soprano saxophone).
In opera, subdivisions of different kinds of soprano voices are sometimes used. These divisions are more to do with the character of the singers voice and timbre rather than her vocal range. The subclassifications are as follows:
Famous sopranos have often caused opera enthusiasts to divide into opposing "clubs" supporting one singer over another. The rivalry between Maria Callas and Renata Tebaldi, for example, was one of the most famous of all opera (see anecdotes in La Tosca article).
Historically women were not allowed to sing in the Church, so the soprano roles were given to young boys, and later to castrati, who were men whose larynxes had been fixed in a pre-adolescent state through the process of castration.