The term 'Chili Hotness Unit' is a unit of measurement used to measure the spiciness of chili peppers. The crossword solution for this term is 'ALARM, ' which refers to the physical sensation of heat that one experiences when eating a chili pepper. This sensation is often described as an 'ALARM' going off in the mouth, signaling the presence of capsaicin, the compound responsible for the heat in chili peppers.