What are accords? In the perfumery and fragrance world, an accord is what we call a blend of notes to create a new note, or an idea of a scent. These can be molecules and ingredients to create a scent that isn't captured in nature or even what perfumer's call "fantasy" accords--abstract ideas or experiences in scent format.
Such examples of accords are as simple as "green floral accord", "spice accord", or the ever-imaginative fantasy accords like "warm hug", "heavenly clouds" and so on.
Accords help perfumers get closer to the idea of what they're trying to create. In candle making, I use fragrance oils and blend them to get at an idea, recreate a nostalgic moment or find a blend that simply smells great. In my Trail candle, I recreate the experience of being outdoors in the Pacific Northwest with a blend of several fragrance oils that altogether smell like a hike in a damp forest.
Think of accords like notes on a piano. A single piano key is one fragrance note. Played alone, you would only smell one particular smell. Play several at once and you have an entirely different experience.