Chord

When an uncovered square with a number has exactly the correct number of adjacent squares flagged, performing a click with both mouse buttons on it will uncover all unmarked squares; This is called a Chord.

It is a basic technique that allows players to clear squares using flags, and the reason why flagging styles are often more efficient than non-flagging ones.

Using the middle mouse button will also cause a chord.

Usually, chords are performed as 1.5 clicks.