Hidden Pair
Column 5 has two cells highlighted in blue at H5 and I5. Both of these cells contain the candidates 3 and 9, but the candidates 3 and 9 do not appear in any other cell of column 5. Therefore 3 and 9 must provide the solutions for the highlighted cells. The other candidates in these cells are highlighted in magenta, and may be removed.

Hidden pairs can also appear in rows and boxes.