Which of the following best describes Celsius?

Celsius is best described as a scale based on the freezing and boiling points of water. The Celsius scale sets the freezing point of water at 0 degrees and the boiling point at 100 degrees under standard atmospheric pressure. This direct relationship to water's physical properties makes it particularly intuitive for everyday use, as these are commonly encountered temperatures in nature.

While it is true that Celsius is commonly used in scientific contexts, its foundation is specifically tied to the behavior of water, making the reference to its freezing and boiling points the most accurate description among the given choices. Absolute temperature scales, like Kelvin, measure thermal energy starting from absolute zero and are not based on water's properties. The mention of measuring heat in space does not apply specifically to Celsius, as this scale pertains to temperature measurement rather than direct heat measurement or its properties in the context of space.