From the Super Mario Wiki
A Dash Space is an uncommon space only present in Mario Party 9. When a player lands on a Dash Space, he or she will get to roll an extra time with the Dice Block. If a Captain lands on another Dash Space after he or she lands on a Dash Space, then the Captain still get to roll the Dice Block an extra time. Special Dice Blocks cannot be used by the Captain landing on the Dash Space, however.
Dash Spaces also appear during several Captain Events. This includes Scaredy Rat Race, in which the Scaredy Rat rolls 1-3 Dice Blocks instead of the standard 1-6 Dice Blocks after landing on these spaces.