1. The question asks: "What is a K cell?" 2. A K cell is a type of immune cell known as a "killer cell" or more specifically a Natural Killer (NK) cell. 3. NK cells are part of the innate immune system and play a crucial role in the body's defense against tumors and virally infected cells. 4. They can recognize stressed cells in the absence of antibodies and MHC, allowing for a faster immune reaction. 5. NK cells kill target cells by releasing cytotoxic granules that induce apoptosis (programmed cell death). 6. In summary, a K cell is an immune cell specialized in killing harmful cells to protect the body.