Naked Pair
Intermediate Removes candidates Used in: Sudoku, Killer Sudoku, Calcudoku, Futoshiki
Two cells in the same unit show the same two candidates and nothing else — say {2,5}. Between them they will use up both of those digits, so 2 and 5 can be erased from every other cell in that unit. You haven’t placed a digit, but you’ve sharpened the whole unit.
How to spot it
Look for two cells in the same unit showing the identical pair of candidates and nothing else.
What you can conclude
Those two digits are reserved for those two cells — erase them from every other cell in the unit.
Worked example
Two cells in a row both read {2,5}. Another cell in the row reads {2,5,7}; since 2 and 5 are spoken for, it must be 7.