What is a countertenor?
A countertenor is a male singer who can sing as high as a soprano or mezzo-soprano. The countertenor is the rarest of all voice types.
The countertenor was not originally an operatic voice type as historically it was the castrati who would sing the female operatic roles in an age when it was not proper for women to sing in the opera. Instead, countertenors were popular in religious choirs where women were also not allowed to participate.
Today the countertenor is arguably the most profitable voice type, mainly due to rarity and lack of competition at auditions. Many baroque operas utilise the countertenor today due to many being written for castrati singers. The opera Giulio Cesare by Handel requires 4 countertenors to replace the castrati singers. Some modern operas also cast countertenors, such as Jonathon Dove's Pinocchio which really showcases the intricacies of the voice type.
It's easy to mistake yourself for a countertenor as all male voices have an area in the voice called the falsetto. This is a high pitched area, usually quieter and softer in tone than the main voice. If the singer has trained his falsetto range well it can easily be mistaken for a countertenor voice.