Mane 6 

The name given to the group of ponies who include: Twilight Sparkle, Rarity, Apple Jack, Pinkie Pie, Rainbow Dash and Fluttershy; the 6 main characters of the show My Little Pony: Friendship is Magic.

Main is spelt as Mane because most names in My Little Pony are a play on words with relation to ponies or horses. So the word mane is used not only to describe the 6 main characters of the show but also is the hair on the heads and back of the necks of ponies/horses.

"OMG I just love the mane 6 in MLP"

Person 1: "So who is your favourite pony in MLP:FiM?"
Person 2: "I don't have a favourite; I love the mane 6!"

Mane 6 by Rarity is Best Pony June 7, 2013

Mane 6 

Referring to My Little Pony - Friendship is Magic

The Mane 6 are the 6 main characters of this show, however the wordgame with "mane" has been evidently created by the Bronies, see Brony.

Their names: Twilight Sparkle, Rainbow Dash, Rarity, Applejack, Pinkie Pie, Fluttershy.

Brony 1: Hey, who's your favourite of the Mane 6?
Brony 2: Pinkie Pie, of course!
Brony 3: Well, mine's Rainbow Dash.

Mane 6 by KuroNightShadow June 18, 2013