Aneuploidy is the condition of having an abnormal number of chromosomes. One of the more common types of aneuploidy is Klinefelter's syndrome, in which a person is born with an extra chromosome, resulting in anomalies like an XXY pair in males. This frequently causes the male to have reduced fertility, and sometimes even to result in an intersexed individual.
One such individual is the famous Caroline Cossey, who was born male but got gender reassignment to female after a troubled childhood and the revelation that she had Klinefelter's. She went on to become an actress and model, and even to be one of the female companions to James Bond in the movies.
Here's a photo of Cossey to help you remember "aneuploidy":
