Temperature is a measurement used to express hot or cold in terms of numbers. You may encounter the use of temperature in many different everyday things such as describing the weather (how hot or cold it is outside), cooking, body temperature to check if you have a fever, and more.
There are various measurements of temperature. The most common temperature scale used is the Celsius (°C) scale, which is used in the metric system of measurement. The Celsius scale is used in most countries around the world.
The United States primarily uses the Fahrenheit (°F) scale instead of the Celsius scale. Both scales have used the freezing and boiling points of water as reference points. The definition of the Celsius scale no longer uses these points as part of its definition, but they are still frequently used as reference points. Temperature is commonly measured using a thermometer. Below is a thermometer showing these reference points in both the Celsius and Fahrenheit scales.
The Kelvin scale is another temperature scale that is mostly used in scientific contexts. Rather than using degrees like Celsius and Fahrenheit, the size of each unit in the Kelvin scale is simply 1 kelvin, rather than "one degree kelvin." Also, unlike the Celsius and Fahrenheit scales, the Kelvin scale is not really used for everyday purposes. People do not normally measure how hot or cold it is outside in kelvins, and you are unlikely to find any recipe that would tell you to preheat your oven to 422 kelvins.