The arrangement of veins and the veinlets in the lamina of leaf is termed as venation.
When the veinlets form a network, the venation is termed as reticulate (Reticulate Venation). When the veins run parallel to each other within a lamina, the venation is termed as parallel (Parallel Venation). Leaves of dicotyledonous plants generally possess reticulate venation, while parallel venation is the characteristic of most monocotyledons.
Fig: Reticulate Venation, Parallel Venation