Final answer:
Polyploidy refers to organisms that have three or more sets of chromosomes, which can lead to larger and more robust plants and reproductive isolation in some cases.
Step-by-step explanation:
Polyploidy is best defined as the presence of three or more sets of chromosomes. It is a condition frequently seen in plants where an organism has extra sets of chromosomes beyond the typical two sets found in diploid species. This can occur naturally through mechanisms such as errors in meiosis or through hybridization events where gametes from different species combine. Polyploidy can lead to reproductive isolation, as polyploid organisms, especially if they are autopolyploid, might not be able to interbreed with the normal diploid members of their species. Polyploidy can result in larger and more robust plant individuals compared to their diploid counterparts. In contrast, polyploid animals are exceedingly rare and are typically sterile due to complications during meiosis.