If we view the story of a perfume the same way we would the development of a piece of classical music, an accord is what happens when all the individual parts are played together. It creates a seamlessly lovely sound that could never be achieved with just one instrument and doesn't really sound like any one of them. More technically, the accord is the combination of three or more notes to create the "body" of a scent. (The notes may be vanilla absolute, roasted cacao, and musk, but you say it smells like a malted milk ball).
An accord can be totally different from its individual notes, and a great perfumer can combine scents in ways that will floor you. CB I Hate Perfume makes a line of fragrances categorized by their accords instead of their notes, each of which comes with a literal story to describe the overall scent. Even though Fall has come and gone, I'm fascinated by the brand's M3 November ($75), which purportedly smells like the perfumer's rainy November reflections about a book read on a similar late autumnal day many years before.