A diminished chord or arpeggio is on that has a flat 5 and a flat 3. As a bass player you will at some stage be called to play over a diminished chord and you'll be well prepared if you remember the diminished triad theory and these two arpeggios.
The first diminished arpeggio is a passive variation moving down the neck and the second diminished arpeggio variation is one that moves up the neck but still in one position. The second Diminished arpeggio is easier to play as it in a single position, but might not be the flavor you want to have. Try them out and read more. Below are the graphics of the two arpeggio variations with TAB, notation and graphic frame.