Glossary
What is density altitude?
Pressure altitude corrected for temperature: the altitude the air feels like to the wing, the propeller and the engine. Heat, humidity and field elevation all push it up, and when it is high the airplane climbs worse and needs more runway than the same airplane on a cold day at sea level.
That is the whole entry for now. The longer version, with the mechanics and worked examples, is still to be written. See autorotation for how those read once they exist.