What is "diminished triad"

n. (context music English) a triad that has a diminished fifth between the bottom note and the top note

In music, a diminished triad , also known as the minor flatted fifth (m5), is a triad consisting of two minor thirds above the root — if built on C, a diminished triad would have a C, an E and a G. It resembles a minor triad with a lowered ( flattened) fifth. It can be represented by the integer notation {0, 3, 6}.

In the common practice period, the diminished triad is considered dissonant, or unstable, because the dissonant diminished fifth symmetrically divides the octave. The lack of tonal center or stability, possession of a leading-tone, and the dominant function give the chord drive.