Natural Killer Cells (NK cells) are a type of white blood cell that play a crucial role in the body's immune response. They are part of the innate immune system, which means they provide a rapid defense against infections and tumors without needing prior exposure to a pathogen. NK cells can recognize and destroy infected or cancerous cells by releasing toxic substances. These cells are unique because they can identify stressed or abnormal cells through specific receptors. When they detect these cells, NK cells release chemicals that induce cell death, helping to control infections and prevent the spread of tumors. Their ability to act quickly makes them essential for maintaining overall health.