When two cells in a house hold only the same two candidates, no other cell in the house can use those two digits.
On an Arrow board this works exactly as in Classic. The examples are from Arrow puzzles on this site. The arrows often make the pair, by cutting a cell down to two candidates.
Worked examples
A position from a real Arrow puzzle on this site. Step through it: the board lights what each step talks about, and the red lines show what rules what out.
A pair in a column
In column 3, look for two cells that hold the same two candidates between them.
Where it fits
HardNaked Pair is a Hard technique: Hard Arrow puzzles are the first to need it.
The Classic Naked Pair lesson teaches it on a plain 9×9 board. The Arrow overview explains the rule and the levels.
Naked Pair in the other styles: Sudoku X, Jigsaw, Thermo, Windoku, Kropki.
Try it on a Hard Arrow puzzle. Next Step points it out when it is the move.