You thought it was about… but learned it was about.

[cheerfulgreek]

It’s about having sex. Ray Charles had a song called “Night time is the right time” — a more obvious song. “Afternoon Delight” is more like “When it’s right, it’s right” is the right time, so if that happens to be during the day then during the day it is.

The online meaning:
“Afternoon Delight is the name of a 1976 song by the Starland Vocal Band. The song, which contains innuendo about casual daytime sex (or an afternoon delight) was a hit. Because of the song’s popularity, afternoon delight has become well-recognized as a term for a midday sexual encounter, often between or instead of scheduled events.”