Botanically, the term describes an arrangement of discrete structures (such as leaflets, veins, lobes, branches, or appendages) arising at multiple points along a common axis. For example, once-divided leaf blades having leaflets arranged on both sides of a rachis are pinnately compound leaves. Many palms (notably the feather palms) have pinnately divided leaves. Most species of ferns have pinnate or more highly divided fronds, and in ferns the leaflets are typically referred to as "pinnae" (singular "pinna"). Plants with pinnate leaves are sometimes colloquially called "feather-leaved".
Definition adapted from URL: http://en.wikipedia.org/wiki/Pinnate_leaf