K cell - Definition

A K cell (or a killer cell) is a lymphocyte with immunoglobulin Fc receptors, which allow it to bind to and kill antibody-coated cells by antibody-dependent cell-mediated cytotoxicity (ADCC). Once bound the cells act like T cells and "program" the target cell to "self-destruct" by apoptosis.

K cells are probably a sub-set of NK cells.