Division of a leaf blade into leaflets arranged on each side of a common leafstalk.
when the leaflets are dispersed laterally along the rachis of a compound leaf
A compound leaf with the leaflets arranged along the sides of a common axis.
Leaves which are divided up like a feather are said to be pinnately compound.
Leaves divided to the midrib; the leaflets or pinnae are arranged like the parts of a feather on the rachis.