A eunuch is a castrated man. His genitals have been removed. This can be cutting off the testicles.[1] The term "castration" is sometimes used to refer to emasculation where both the testicles and the penis are removed together.
Over the millennia since, eunuchs had a lot of different functions in different cultures such as domestics, treble singers, religious specialists, government officials, military commanders, and guardians of women or harem servants. When eunuchs ran a harem, a monarch could be sure he was the one who fathered his wives' children since eunuchs were always infertile.
In Byzantineart, angels and eunuchs were often shown in a similar light and manner.[2]