What is Temperature and why is it important in aviation?

Temperature is the warmness and coldness of air that we feel around us.
Different weather fronts, depending on their origin bring in different air masses.
If they come from northern latitudes/regions, they usually bring cool/colder air with them.
Ex: Polar Air (north/south pole)
If they come from southern latitudes/regions, they usually bring warmer/hot air with them.
Ex: Hot Desert Air (Sahara)

Temperature is important in flying as it decides the density of air and thus the engine’s performance.
This relates to reciprocating (normally aspirated) engine only.
Warmer or hotter air is comparable to air at higher elevations/altitudes and will result in less density,
so less performance.
Cooler/Colder is usually denser, so better performance.