Roundworms are a type of parasitic or free-living worms belonging to the phylum Nematoda. They have long, cylindrical bodies that are tapered at both ends. Roundworms can be found in various environments, including soil, freshwater, and marine habitats. Some species are beneficial for ecosystems, while others can cause diseases in plants, animals, and humans. In humans, roundworms can lead to infections such as ascariasis, which is caused by the Ascaris lumbricoides species. These infections often occur in areas with poor sanitation and can result in symptoms like abdominal pain and malnutrition. Proper hygiene and sanitation practices are essential to prevent roundworm infections.