Ripple mode is a state that affects the behavior of all delete, move and trim operations, it can be toggled on/off via the button on the timeline toolbar :
Any operations performed while ripple mode is on are rippled throughout the rest of the timeline so that any gaps created by the operation are closed. If ripple mode is turned off then a gap/filler will be left on the track in place of any segments that have been removed or trimmed down. See below.
Ripple mode does not apply to splice and overwrite operations because these operations are inherently rippled (splice) or not (overwrite).
The following example shows the effect of deleting the middle of three segments, with and without ripple mode on.
Select the middle segment and press the delete key on keyboard :
Ripple Mode Off
With ripple mode off, the gap remains.
Ripple Off - gap remains
Ripple Mode On
With ripple mode on, the segment to the right is shifted left and closes the gap.
Ripple On - segments collapse and fill gap