love song; love poem
A song or poem about love. The cross-reference 恋歌 is a synonym with a more classical or literary feel.
See also: 恋歌
彼女のために恋の歌を作った。
I wrote a love song for her.
この恋の歌はとても切ない。
This love poem is very poignant.
Compound of 恋 (love) + の (possessive particle) + 歌 (song/poem). The exact historical derivation is straightforward.