The starting grid is a grid that is in rows of 2 or more in racing games. Each position is determined by a qualifying time at the end of a time trial and the fastest time will receive the pole position when the race starts. In the Mario Kart franchise, the starting grid is in 4 rows of 2, then 2 rows of 4, and now 4 rows of 3 (depending on the game you're playing).
The finishing positions from the last race during Grand Prix or Versus mode will be the new grid for the next one. The grid is also very useful during a standing start, which keeps all of the cars at their rightful positions while waiting for the green light to commence racing.