A drafting grid is a set of infinite perpendicular or parallel lines drawn with regard to an object. A grid helps drafting when you need to draw, for example, objects at specified distances from (parallel) or at certain positions along (vertical) a concrete object.
When you construct a grid on an object, the object remains intact: it is neither split nor broken.
You can construct a grid on a straight line or an arc. When constructing a grid, you can draw both its horizontal and vertical lines at once.
A good example for using a grid is when drawing box dividers that need to be positioned at equal distances along a line. You can use a grid, draw a divider at one of the sections, and then translate the drawn object along the line at the rest of the intersections between the object and the grid lines.
A five-line grid was added to a rectangle's lower line, dividing it into four sections. Then a divider was drawn at one of the crosspoints, which was then copied to the other two.