The baseline temperature for the Kelvin scale is absolute zero, defined as 0 Kelvin (K). This temperature corresponds to -273.15 degrees Celsius, where molecular motion theoretically ceases. The Kelvin scale is used primarily in scientific measurements and thermodynamics because it provides an absolute reference point for temperature, allowing for more precise calculations in physical equations. It is essential in various fields, including physics, chemistry, and engineering, where temperature changes significantly affect various processes.