Example of a Buried Double
This is a screenshot
Buried Double: Two Squares in the same Row, Column, or Box that contain the same two Possibles - and the Possibles occur nowhere else in that same Row, Column, or Box.

In this example, the Buried Double is the two Squares containing the Possibles 1 and 4 (coloured cyan). These two Squares MUST contain 1 or 4. Therefore they cannot contain any other Possibles. The 2, 5 (two occurances), 6 and 8 outlined in orange are impossible solutions and can be removed.