An afterglow is the light that remains after the light source has disappeared from view. For example, the glow that remains at dusk after the sun has set below the horizon is an afterglow.
The word afterglow can also refer to a remnant of the pleasure of a happy experience after that experience is over.
Huh. And all this time I thought that afterglow referred to only the pleasure that shows on one’s face upon the end of a particularly good sexual experience. Live and learn. And maybe bemoan in hope, but that’s another story.