From the Super Mario Wiki
The Back Space (also called Reverse Spaces) is a space in the Mario Party series. In Mario Party 3, it only appears in Duel Boards. If the player lands on this space, a dice block appears and the number the player hits will be the amount of spaces the player will have to go backwards. Landing on one in the board Backtrack makes players go in the opposite direction and change the positions of their partners. The Back Space also reappears in Mario Party 9 with a new design and serves the same function. In Mario Party: Island Tour, its design is different again, they only appear on Kamek's Carpet Ride and the player has to go back the number of spaces in it. The Back Space reappears in Mario Party 10 with the same purpose as in Mario Party 9.
On the results screen in Mario Party 3, the Back Space is referred to as the "Reverse Space".
Name in other languages
||Case retour (MP3)
Case demi-tour (MP9)