Definition: A measure of Kinetic Energy, also an indirect measure of how hot something is.
Temperature is a measure of kinetic energy in matter, but is commonly interpreted as how hot or cold something is. Temperature can be measured in many different ways, the most common ways we see in the United States are Fahrenheit or Celsius. A thermometer is a device that measures how hot something is, by telling us its temperature. I will have some formulas at the bottom of the page that will help you convert temperatures from one format to another.
In thermodynamics, temperature is almost directly a measure of thermal energy . All atoms are constantly moving at some speed, bouncing around and off of one another in a very small space while they are held together by atomic bonds. Some atoms move much faster than others. Faster movement means that there is more energy there, which usually ends up meaning that the molecule is less stable and therefore hotter.
Put very simply, the faster the atoms move, the hotter something gets. This also explains why colder things are denser and heavier than hotter things. The colder something gets, the less the atoms are moving, so they group closer and closer together. This means cold things are denser and heavier because they allow less space between the atoms for other atoms to get in.
There are limits to how hot and how cold anything can get, although both of these are theoretical temperatures. The coldest anything can ever get is called Absolute Zero or Absolute Cold, which means that the atoms in the molecule aren’t moving at all. Absolute zero is at a temperature of about -273.15 Celsius or -459.67 Fahrenheit, or very simply 0 Kelvins. Absolute cold is a theory because even in the coldest parts of space, things like Cosmic Radiation keep the temperature from ever being that cold. Space usually has a temperature of around 2.73 Kelvins, or -456.94 Fahrenheit.
There is also a limit to how hot things can be in theory, which is called Absolute Hot. Absolute hot is the temperature of something like a Supernova, which is a star exploding. The actual theorized temperature of absolute hot is:
or about 255,021,300,000,000,000,000,000,000,000,000 Fahrenheit.
And now, some formulas in case you want to convert temperatures!
Fahrenheit to Celsius: Fahrenheit = (Celsius*1.8)+32
Celsius to Fahrenheit: Celsius = (Fahnrenheit*5/9)-32