Parallel venation is a term describing a plant whose leaves have veins that run in parallel. A good example of a type of plant with parallel venation is most types of grasses.
While what pattern the veins in a plant take may not be all that important in itself, it is a good sign of some other facts about the plant. Plants with parallel venation are almost always monocots (meaning they have only one seed leaf), which translates into relativly simple, flowerless, annual plants. <\P>
The other predominate leaf type is pinnate venation.