Ylang ylang is a small, yellow flower that grows from the Cananga tree (via Healthline). It has a "heady, aromatic scent" that is "fruity, flowery, and rich." It's often used in aromatherapy for this reason. As an essential oil, it has the potential to "boost mood, reduce depression, and alleviate anxiety," according to a study published in Scientific Electronic Library Online. Fragrance blog Viroa London describes the smell of ylang ylang as a "rich and sensual floral scent" that "also has subtle buttery banana tones." Some of the world's most popular perfumes use this ylang ylang as a floral note in their scents, including Gucci's Bloom Profumo di Fiori and Gorgeous Gardenia, Tom Ford's Soleil Blanc and Black Orchid, and Dior's J'adore (via Who What Wear).
According to Who What Wear, ylang ylang is usually paired with "classic scents" like "vanilla, rose, and jasmine" to boost floral fragrance. So if you're wearing a floral scent, chances are ylang ylang is in there somewhere.