Medical Definition of T cell
: any of several lymphocytes (as a helper T cell) that differentiate in the thymus, possess highly specific cell-surface antigen receptors, and include some that control the initiation or suppression of cell-mediated and humoral immunity (as by the regulation of T and B cell maturation and proliferation) and others that lyse antigen-bearing cells—called also T lymphocyte; see cytotoxic t cell, helper t cell, suppressor t cell, t4 cell
Seen and Heard
What made you want to look up T cell? Please tell us where you read or heard it (including the quote, if possible).