To straighten or stretch s.t. out horizontally; to be stretched out horizontally (as a coil of rope, line, a snake in the road, etc.); to stretch out a line over s.t. or across s.t.
Stretch out a line over your garden so its rows are straight.
Stretch out this line horizontally so we can see how long it is.
That snake is stretched out horizontally in the middle of the road (perpendicular to the road).