A naked single is a cell that can hold only one digit: every other digit is already in its row, its column or its region.
In Jigsaw the region takes the box’s place. Its irregular shape reaches into rows and columns a box would not, so it often rules out the last digits.
Worked examples
2 positions from real Jigsaw puzzles on this site, the familiar case first. Step through each one: the board lights what each step talks about, and the arrows show what rules what out.
Settled by its row and column
Look at row 3. One empty cell here has only one candidate left.
The region settles it
Its row and column alone leave this cell more than one digit. The lit region rules out the rest.
Where it fits
EasyNaked Single is an Easy technique: Easy Jigsaw puzzles are the first to need it.
The Classic Naked Single lesson teaches it on a plain 9×9 board. The Jigsaw overview explains the rule and the levels.
Naked Single in the other styles: Sudoku X, Thermo, Windoku, Arrow, Kropki.
Try it on an Easy Jigsaw puzzle. Next Step points it out when it is the move.