Refers to the pleasant scent of flowers, often used in poetic or descriptive contexts.
The fragrance of flowers is drifting through the garden.
When spring comes, the whole area is filled with the scent of flowers.
Compound of 花 (flower) + の (possessive particle) + 香 (fragrance). The reading か for 香 is a literary or classical reading, giving the word a slightly poetic feel.