A grid is a regularly
repeating pattern of
lines separating some
shape or an entire
plane into small
cells. The most common grid is a
square grid in which 2 sets of
equally-spaced
parallel lines are
perpendicular to each other.
You can also have
triangular grids,
hexagonal grids,
polar grids (which have a set of
concentric circles and a number of lines passing through their common
center), etc.
Often, grids are marked with coordinates.