Thanatology is the scientific study of death, particularly the grief and social attitudes surrounding death.
Data studied various aspects of thanatology while researching the proper way to say goodbye to Ro Laren and Geordi La Forge after it was believed that they were killed in a transporter accident. In Data's research, he revealed that "in almost all societies, it is traditional to say a ritual farewell to those you call friends." (TNG: "The Next Phase")
Thanatology is the main science amongst the Vhnori. Neria was the chief thanatologist of the Vhnori. (VOY: "Emanations")