The traditional sandpile model consists of a set of points arranged in a grid pattern. Each point shares an edge with points to its north, east, south, and west. Thus points on the corners have 2 neighbors, on the edges have 3 neighbors, and all others have 4 neighbors. Each point in the grid has associated with it a number corresponding to the number of grains of sand on the cell.
Variations of this basic model include adding edges to the grid to allow ``wrap-around'', addition of edges to increase the number of neighbors to 8, and 3-dimesional models.