Final answer:
Nondisjunction refers to the failure of homologous chromosomes to separate during anaphase I of meiosis, which can result in gametes with an abnormal number of chromosomes, known as aneuploidy. This can happen in meiosis I or II.
Step-by-step explanation:
The term that refers to the failure of homologous chromosomes to separate during anaphase I of meiosis is nondisjunction. Nondisjunction can lead to the production of gametes that have an abnormal number of chromosomes, a condition known as aneuploidy. If nondisjunction occurs during meiosis I, it results in two gametes lacking the chromosome and two with an extra copy. During meiosis II, nondisjunction affects sister chromatids, which can result in gametes with a missing chromosome, gametes with a normal chromosome number, and a gamete with an extra copy of the chromosome.