X-Wing
X-Wing is a Number Place technique. When a specific number’s candidates in two rows (or columns) exist in only the same two columns (rows), you can eliminate that number from other cells in those two columns (rows).
How to Use X-Wing
Focus on a specific number and check which cells in each row have it as a candidate.
Find two rows where the number appears as a candidate in exactly two columns.
If both rows have candidates in the same two columns, you have an X-Wing.
Eliminate the target number from other rows’ cells in those two columns.
Example
Suppose ‘3’ appears as a candidate only in columns 1 and 7 of row 2, and also only in columns 1 and 7 of row 6. This is an X-Wing. Since ‘3’ must go in either columns 1 and 7 of rows 2 and 6, you can remove ‘3’ from candidates in columns 1 and 7 of all other rows.
Tips for Finding X-Wing
Start by looking for rows (or columns) where a number has candidates in exactly 2 cells. If you find two such rows and the columns match, you have an X-Wing. It doesn’t occur frequently, but when you’re stuck with other techniques, trying X-Wing can sometimes provide a breakthrough.