The term 'DETECTOR' (polygraph) is a device used to measure and record physiological indicators such as blood pressure, pulse, respiration, and skin conductivity while a person is asked a series of questions. The crossword solution for this term is 'LIE, ' which refers to the fact that the DETECTOR is used to detect lies or deception. It is commonly used in criminal investigations, pre-employment screening, and other situations where it is important to determine if someone is telling the truth.