1. combination of simultaneous musical notes to produce chords that have a pleasing effect/forming a pleasing and consistent whole
2. agreement or concord
3. in the Harry Potter books by JK Rowling, harmony is another name for the Harry and Hermione ship (equivalent to celebrity couple names, aka Brad + Angelina = Brangelina. Harry + Hermione = Harmony).
Harmonians, as the followers of this ship are called, believe that Harry and Hermione's friendship had much more potential and depth for a romantic relationship than Ron and Hermione's bickering.
Harmonians, or the Harmony ship, is often referred to as "delusional," and Harmonians are repeatedly told to reread the books by Herons (The Ron and Hermione ship) who think we missed all the anvil sized arguments, aka "hints," between Ron and Hermione that reveal their, um, "sexual" tension, when in fact Harmonians very much acknowledge Heron's "I-hate-you-but-I-really-love-you, push-the-girl-on-the-playground-because-I-really-have-a-crush-on-you-Freudian-psycho-babble-theory thing they have going on, but simply prefer the "love is friendship on fire/love without friendship for it's base is like a mansion built upon the sand" Harry and Hermione could have had going on. Harmonians also respect Hermione enough to want her to be with someone that can actually challenge (intellectually and otherwise) her as a person (Harry), rather than simply challenge her patience (Ron).
Heron shipper: Harry and Hermione are too serious, Ron and Hermione have so much fun together. Ron can make her laugh.
Harmony shipper: You do realize H/Hr are fighting a war against Voldemort and are prepared for the fact that they may die? Yeah, I don't understand why they're so gloomy either... idiots. Oh, and Ron making her laugh... that happened somewhere between making her cry and abandoning her, right? If you're gonna take THAT angle, just get her with a Weasley twin, why don't cha? Idiots.
Heron shipper: Harry and Hermione have a purely platonic, brother/sister relationship.
Harmony shipper: A brother-sister relationship? I have never had Harry and Hermione's relationship with any of my siblings. But, believe it or not, I DO fight and bicker like a 5 year old with them pretty often... GASP! That must mean we are destined to be together! Seriously? And all of you platonic-pushers do realize that Hermione and Ron were platonic too at first, right? They didn't jump into the sack when they were 11. Idiots.
Heron shippers: Hermione is much more attracted to freakishly tall, immature, lazy, intellectually boring, ginger guys that make her cry over her regularly tall, raven-haired, kind, brave and self-sacrificing, emerald-green-eyed best friend!
Harmony shippers: Um. Really?