A path composed of connected horizontal and vertical line segments, each passing between adjacent lattice points. A lattice path
is therefore a sequence of points 
, 
,
..., 
with 
such that each 
is a lattice point and
is obtained by offsetting one
unit east (or west) or one unit north (or south).
The number of paths of length 
from the origin (0,0) to a point
which are restricted to east and
north steps is given by the binomial coefficient 
.
