Definition
A form of energy transferred between substances or systems due to a difference in temperature. Heat flows from a hotter region to a cooler one and is measured in units such as British Thermal Units (BTU) or calories.
Plain English
Heat is energy on the move from something warmer to something cooler. It is not the temperature itself — it is the energy being transferred because of a temperature difference.
Context Anchor
Seen in aircraft systems, engine cooling, cabin heating, weather discussions, and maintenance work involving temperature changes.
Derivation
From Old English hǣtu, meaning warmth. The everyday word stuck, but in physics and engineering it has a stricter meaning: energy in transit, not the warmth a body already contains.
Why Pilots Care
Managing heat prevents engine damage, controls material expansion, and maintains safe operating temperatures in flight.
Grounding Statement
When you touch a hot exhaust pipe and feel your hand warm up, that warming is heat — energy moving from the pipe into your skin because the pipe is hotter.
Intuition Check
Heat does not simply mean “high temperature.” In this context, heat means energy moving because one thing is warmer than another.
Example Sentence 1
The technician inspected the cylinder for cracks caused by repeated heat and cooling cycles during engine operation.
Example Sentence 2
Technicians monitored heat buildup in the avionics bay after extended ground runs.