Naked Pair

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Naked Pair
If two cells in the same group contain exactly the same two candidate values, these candidate values can be excluded from other cells in the group.

In the example below, the Naked Pair is marked by A and B. When cell A is a 4, cell B must be the 5 and vice versa. We do not yet know the values of cell A and B, but we do know that one of these cells must be a 4 and the other a 5. This means that the other cells cannot contain a 4 or a 5 and can therefore be excluded. The candidate values 4 and 5 can be excluded from the yellow cells.
Naked Pair
Naked Triple
The same principle that applies to Naked Pairs applies to Naked Triples & Naked Quads.

If three cells in the same group contain exactly the same three candidate values, these candidate values can be excluded from other cells in the group. The cells which make up a Naked Triple don't have to contain every candidate of the triple. If these candidates are found in other cells in the group they can be excluded.

In the example below, the Naked Triple is marked by A, B and C. We do not yet know the values of cell A, B and C, but we do know that these cells must be a 2, a 7 or an 8. This means that the other cells cannot contain a 2, a 7 or an 8 and can therefore be excluded. The candidate values 2, 7 and 8 can be excluded from the yellow cells.
Naked Triple
Naked Quad
If four cells in the same group contain exactly the same four candidate values, these candidate values can be excluded from other cells in the group. The cells which make up a Naked Quad don't have to contain every candidate of the quad. If these candidates are found in other cells in the group they can be excluded.

In the example below, the Naked Quad is marked by A, B, C and D. We do not yet know the values of cell A, B, C and D, but we do know that these cells must be a 2, a 6, a 7 or a 9. This means that the other cells cannot contain a 2, a 6, a 7 or a 9 and can therefore be excluded. The candidate values 2, 6, 7 and 9 can be excluded from the yellow cells.
Naked Quad