heat

Wikipedia

Noun

heat (countable and uncountable; plural heats)

1. (uncountable, physics) thermal energy

   This furnace puts out 5000 BTUs of heat.

   That engine is really throwing off some heat.

   Removal of heat from the liquid caused it to turn into a solid.

2. (uncountable) The condition or quality of being hot.

   Stay out of the heat of the sun!

3. (uncountable) An attribute of a spice that causes a burning sensation in the mouth.

   The chili sauce gave the dish heat.

4. (uncountable) A period of intensity, particularly of emotion.

   It's easy to make bad decisions in the heat of the moment

5. (uncountable) An undesirable amount of attention.

   The heat from her family after her DUI arrest was unbearable.

6. (uncountable, slang) The police.

   The heat! Scram!

7. (Can we verify this sense?) (uncountable, slang) One or more firearms.
   • 1983 Larry Niven; Jerry Pournelle, Lucifer's hammer‎, page 508:

     You carrying heat?" "You saw me unload the pistol," Hugo said. "It's in the waistband. And the kitchen knife. I need that for eating.

   • 2004 Tom Clancy, The Teeth of the Tiger‎, page 62:

     Evidently, he wasn't carrying heat with him at the time." "Civilized place like Rome, why bother?" Granger observed.

   • 2005 John Sayles, Pride of the Bimbos, page 187:

     Pogo Burns is not a guy who likes to be threatened with a rifle. Especially when it's for no good reason. You never show heat unless you plan to use it.

   • 2007 Brian Groh, Summer People, page 234:

     "I should have brought some heat for you." "Heat?" "A burner, man, a gun."

   • 2008 James Swain, The Night Stalker, page 92:

     Both were carrying heat, and I slipped their pieces into my pants pockets.

8. (countable, baseball) A fastball.

   The catcher called for the heat, high and tight.

9. (uncountable) A condition where a mammal is aroused sexually or where it is especially fertile and therefore eager to mate.

   The male canines were attracted by the female in heat.

10. (countable) A preliminary race, used to determine the participants in a final race

    The runner had high hopes, but was out of contention after the first heat.

11. (countable) One cycle of bringing metal to maximum temperature and working it until it is too cool to work further

    I can make a scroll like that in a single heat.

12. (countable) A hot spell.

    The children stayed indoors during this year's summer heat.

In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body.

A related term is thermal energy, loosely defined as the energy of a body that increases with its temperature. Heat is also loosely referred to as thermal energy, although many definitions require this thermal energy to actually be in the process of movement between one body and another to be technically called heat (otherwise, many sources prefer to continue to refer to the static quantity as "thermal energy").

Energy transfer by heat can occur between objects by radiation, conduction and convection. Energy can only be transferred by heat between objects - or areas within an object - with different temperatures (as given by the zeroth law of thermodynamics). This transfer happens spontaneously only in the direction of the colder body (as per the second law of thermodynamics). The transfer of energy by heat from one object to another object with an equal or higher temperature can happen only with the aid of a heat pump via mechanical work or by using mirrors or lenses to focus radiation which thereby increase its energy flux density.