K-type refers to the type of thermocouple that the thermometer uses. A thermocouple is a type of sensor that measures heat. Thermocouples consist of two wires made from different metals joined at the end to form an electrical junction. Type K thermocouples provide the widest temperature range. They are the most common type. You may also come across types J, T, E, N, S, R, and B, which all have various temperature ranges and service lifetimes.