Noun, pl. Chiasmata
Thought to be the point where two homologous non-sister chromatids exchange genetic material during chromosomal crossover during meiosis (sister chromatids also form chiasmata between each other, but because their genetic material is identical, it does not cause any change in the resulting daughter cells). (wikipedia.org)
2. A point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands. (Google Dictionary)
3. The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over like the letter X. (biology-online.org)
Word origin: Modern Latin, from Ancient Greek χίασμα, from χίαζειν (“to mark with the letter chi”).