A polyploid was an individual with more than two copies of their chromosomes. Humans and most mammals inherited one copy of each chromosome from their mothers and one copy of each chromosome from their fathers, but some microbes, plants, fish, and amphibians inherited more than one copy from each of their parents, giving them three or more copies of each chromosome.
Dr. Culber suggested to Adira that Su'Kal may be a polyploid, noting that proper chromosome separation may have been disrupted in him due to radiation. (DIS: "That Hope Is You, Part 2")