Shipping, thought to derive from "relationshipper" is something that happens when a fan looks at a work of fiction and sees a relationship, almost always romantic or potentially romantic, that isn't explicitly present in the original work.
I first encountered The Magic Flute in Bergman's 1975 film version, in which Pamina is spirited away from her vengeful and imperious mother, the Queen of the Night, by her father, the kindly Sarastro.
It's a wonderful, magical production.
I only recently discovered that almost none of this back story was in the original libretto. Pamina was abducted by Sarastro, but there was no indication that he was her father, or that, as follows from that implication, that he and the Queen of the Night once had a history together. In the original libretto Sarastro explicitly isn't her father. At least, he isn't her father according to the Queen of the Night, who is a knife-crazy vengeful psychomom and not necessarily a reliable narrator.
So Bergman the Mozart fan shipped Sarastro and the Queen of the Night. And it works, dramatically, better than canon.
In the original, Sarastro simply abducts Pamina because her mother, a powerful sovereign, is an unfit parent. And she wants Pamina to kill Sarastro because he was given a magical MacGuffin, a sun-disk amulet, by Pamina's father, and she needs it very badly. It is, in the original libretto, the reason why, having gotten into the same room with Pamina, she doesn't just take her with her when she leaves.
Writing that reminds me again why Schikaneder's mad librettist skills are usually mentioned last in his list of lifetime achievements.
Branagh bought into the same idea. Sarastro and the Queen of the Night were once, well, more than friends.
As emotionally and dramatically effective shipping goes, it ranks with James Goldman's shipping Robin Hood with the Pryoresse of Kyrkely.