What, exactly is "temperature"?

[Comrade-Soupbeans]

Is it the average annual temperature or something else?

I'm trying to gauge the climate of a specific place on one of my maps and realized i don't know specifically what is meant when the map says somewhere is "X degrees Celsius" on the temperature layer. Being able to plop down a burg and see more specific data is great, but i'd like to know what i'm seeing when doing a quick glance at temperature layer

[Azgaar]

Yes, it's an average annual temperature.