The lower mordent (German, Mordent) consists of the principal note, the note of the scale below (unless otherwise indicated),
and the principal note again, played as rapidly as possible in the time of the principal note; the third note should be of longer duration than the preceding ones, and should bear the accent
When an accidental is placed below the lower mordent sign, it signifies that the lower note is to be raised or lowered a semitone.
In Baroque music the short appoggiatura is sometimes combined with the lower mordent.
When the lower mordent is placed before a chord, it only affects that particular note before which it is placed.