The Celsius scale is a temperature scale that is based on the freezing and boiling points of water at sea level. The degree Celsius (°C) is defined as 1/100th of the difference between the freezing point and boiling point of water. The freezing point of water is defined as 0°C, and the boiling point of water is defined as 100°C.

The Celsius scale is used in most countries around the world, except for the United States and a few other countries that still use the Fahrenheit scale. The Celsius scale is also used in scientific research, as it is the standard temperature scale for most scientific measurements.

The Celsius scale is a convenient scale to use because it is based on two easily reproducible reference points. It is also a linear scale, which means that the difference between two temperatures in degrees Celsius is the same as the difference between those two temperatures in any other temperature scale.

The Celsius scale is also used to measure temperatures below the freezing point of water and above the boiling point of water. For example, the temperature of liquid nitrogen is -196°C, and the temperature of the Sun's surface is about 5,778°C.

The Celsius scale is named after the Swedish astronomer Anders Celsius, who proposed the scale in 1742.