Mordent
A mordent (indicated by 
or a prall 
with a line through it) is a similar decoration as a pralltriller. The difference is that a mordent uses the note below the note to decorate. You use the keyboard shortcut <m> or the trill menu to enter.
Depending on tempo, a mordent is played differently as given above two possibilities. A mordent will be played according to the ornamentation settings (slow/fast, diatonic/chromatic, baroque).