Polyploidy refers to organisms that have more than two complete sets of chromosomes. It occurs commonly in plants but rarely in animals. Polyploidy can be induced artificially through chemicals like colchicine to double chromosomes. There are different types of polyploidy including autoploidy which involves multiple sets from the same genome, and allopolyploidy which combines genomes from different species. Polyploidy has various applications in plant breeding as it can create seedless fruits, increase vigor, restore fertility in hybrids, and enhance stress tolerance. While it provides advantages, polyploidy can also lead to issues like reduced fertility and complex inheritance patterns.