Final answer:
The SI unit for temperature is the Kelvin (K), an absolute scale without a degree symbol, contrasting with the relative Celsius and Fahrenheit scales.
Step-by-step explanation:
The SI unit used for measurements of temperature is the Kelvin (K). This unit is part of the International System of Units (SI), which is the modern form of the metric system. The Kelvin scale is an absolute temperature scale where 0 K (zero Kelvin) represents the lowest theoretical temperature, known as absolute zero. Unlike the Celsius and Fahrenheit scales, which are relative temperature scales, Kelvin does not utilize a degree symbol; therefore, its unit is simply written as 'K' without a degree sign.