Sunrise and Sunset refers to the time of the day when the light of the Sun rises from or sets into the horizon. The Round Earth model describes sunset as the spherical earth rotating into the Sun. The Flat Earth model describes sunset as the light of the Sun setting into the Flat Earth.
In accord with what we see, we do not observe a spherical Earth rotating into a Sun. We do not see the horizon rising upwards into the sun. This is a proposed illusion. The most direct description of what we observe is that the light of the Sun is setting into a Flat Earth.