Noon by your clock. The marked body is the Sun, and the line up from due south through the point overhead is your meridian. The Sun is probably not on it: your clock keeps a whole zone's time, and the Sun crosses your meridian when it is ready.
Every day of this year: when the Sun actually crosses your meridian, by your clock. The line wanders a quarter of an hour either way, the equation of time, and jumps an hour at summer time. Where it crosses 12:00, a sundial agrees with your clock.
Now open the clock out to the whole day. Sunrise and sunset split out of noon, half the day's light either side of it. Around the shortest day noon itself is sliding later, so the evenings start to draw out before the mornings do: the earliest sunset comes first.
The same wandering noon, on the sky: the Sun at one mean time every day for a year is the analemma, and its width is that line. It comes from the Earth's elliptical orbit and its tilted axis; the Analemma lesson takes the two apart.