Hydrogels are a class of materials that have the ability to absorb and retain large amounts of water or biological fluids. They are composed of a three-dimensional network of polymer chains that can swell in the presence of water without dissolving. Hydrogels have a wide range of applications in various fields such as biomedicine, drug delivery, tissue engineering, and agriculture. They can be designed to have specific properties such as biocompatibility, biodegradability, and mechanical strength, making them versatile materials for various applications.