Sigh…first draft got eaten by tumblr, so I’ll try again.

The closest thing I can think of to an official term for them is that Melisandre refers to them, obliquely, as shadow sons:

“Is the brave Ser Onions so frightened of a passing shadow? Take heart, then. Shadows only live when given birth by light, and the king’s fires burn so low I dare not draw off any more to make another son. It might well kill him.“ (ASOS) 

At some times, Melisandre suggests that this is the work of R’hllor – “The Lord of Light in his wisdom made us male and female, two parts of a greater whole. In our joining there is power. Power to make life. Power to make light. Power to cast shadows.” – but I think this is a case of Melisandre propagandizing for her religion by attributing the magic known as shadowbinding to her god. 

To test this, I’ve looked for examples of shadowbinders who lack her religious affiliations doing things that Melisandre does. For example, Bloodraven is accused of using shadow assassins: “A shadow came at his command to strangle brave Prince Valarr’s sons in their mother’s womb.” (Mystery Knight) Now, this is most likely mere slander, but it does suggest that there is enough folk lore about shadow assasins out there that people think it’s a thing that magic can do.

Moreover, there is evidence that Bloodraven does have some knowledge of shadowbinding. In Mystery Knight, he pretty clearly uses shadowbinding to disguise himself as Ser Maynard Plumm:

“Distantly,” confessed Ser Maynard, a tall, thin, stoop-shouldered man with long straight flaxen hair, “though I doubt that His Lordship would admit to it. One might say that he is of the sweet Plumms, whilst I am of the sour.” Plumm’s cloak was as purple as name, though frayed about the edges and badly dyed. A moonstone brooch big as a hen’s egg fastened it at the shoulder

…Through the rain, all he could make out was a hooded shape and a single pale white eye. It was only when the man came forward that the shadowed face beneath the cowl took on the familiar features of Ser Maynard Plumm, the pale eye no more than the moonstone brooch that pinned his cloak at the shoulder.

This is almost identical in fashion to the glamour that Melisandre uses to disguise Mance Rayder and Rattleshirt in ADWD: 

Rattleshirt sat scratching at the manacle on his wrist with a cracked yellow fingernail…The big square-cut gem that adorned his iron cuff glimmered redly. “Do you like my ruby, Snow? A token o’ love from Lady Red.”

“The glamor, aye.” In the black iron fetter about his wrist, the ruby seemed to pulse. He tapped it with the edge of his blade. The steel made a faint click against the stone. “I feel it when I sleep. Warm against my skin, even through the iron. Soft as a woman’s kiss. Your kiss. But sometimes in my dreams it starts to burn, and your lips turn into teeth. Every day I think how easy it would be to pry it out, and every day I don’t. Must I wear the bloody bones as well?” (ADWD)

Melisandre associates these glamors with both R’hllor and shadows: “with whispered words and prayer (emphasis mine), a man’s shadow can be drawn forth from such and draped about another like a cloak.” By contrast, Bloodraven’s glamor is associated with shadows but not with R’hllor.

Another possible use of shadowbinding is that Quaithe the Shadowbinder appearing as an illusion to Dany: 

“They sleep,“ a woman said. "They all sleep.” The voice was very close. “Even dragons must sleep.”
She is standing over me. “Who’s there?” Dany peered into the darkness. She thought she could see a shadow, the faintest outline of a shape. “What do you want to me?”
“Remember. To go north, you must journey south. To reach the west, you must go east. To go forward you must go back, and to touch the light you must pass beneath the shadow.” (ASOS)

A woman stood under the persimmon tree, clad in a hooded robe that brushed the grass. Beneath the hood, her face seemed hard and shiny. She is wearing a mask, Dany knew, a wooden mask finished in dark red lacquer. “Quaithe? Am I dreaming?” She pinched her ear and winced at the pain. “I dreamt of you on Balerion, when first we came to Astapor.”
“You did not dream. Then or now.” (ADWD)

Now, it’s possible that this is actually a glass candle in action (”the sorcerers of the Freehold could see across mountains, seas, and deserts with one of these glass candles. They could enter a man’s dreams and give him visions, and speak to one another half a world apart, seated before their candles.” (AFFC)), since Quaithe mentions the glass candles but is also associated with shadows.