Grids are two-dimensional arrays of lines similar to graph paper, except that you can adjust the spacing and other features of the grid to the needs of your work.
One grid establishes the pitch of the boat, another the pitch of the ship
Different grids let you build objects with various orientations.
Grids have these primary uses:
3ds Max provides two kinds of grids: the home grid and grid objects. In addition, it includes the AutoGrid feature, an automated way of creating grid objects.
The home grid is defined by three planes along the world X, Y, and Z axes. Each of these axes passes through the world coordinate system's origin point (0,0,0). The home grid is fixed; it cannot be moved or rotated.
See Viewing and Navigating 3D Space for a complete introduction to the home grid.
A grid object is a helper object you can create whenever you need a local reference grid or construction plane somewhere other than the home grid.
This feature lets you create new objects and grid objects off the surfaces of other objects on the fly. See AutoGrid.