Naked Pair, Triple and Quad

If two cells in a unit both have only the same two candidates, say 3 and 8, then those two digits must fill those two cells, in some order. Remove 3 and 8 from every other cell in that unit. That is a Naked Pair.

The idea extends: three cells whose candidates together are only three digits form a Naked Triple, and four cells with four digits a Naked Quad. The cells do not need to hold every digit of the set: {1,2}, {2,3} and {1,3} work, and so does {1,2,3}, {1,2}, {2,3}.

Notation

Naked Pair: 5 can be removed from r5c2.