The term frond refers to a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the large leaves of cycads and palms (Arecaceae)

When most people use the word frond they mean a large, compound leaf, but if the term is used botanically to refer to the leaves of ferns, it may be applied to smaller and undivided leaves.

Fronds, like all leaves, usually have a stalk called the petiole supporting a flattened blade, sometimes called a lamina. However, fronds are often described using distinctively different terms. The petiole of a frond is called a stipe and the continuation of the stipe into the blade portion is called the rachis. The blades may be simple (undivided), pinnatifid (deeply incised, but not truly compound), pinnate (compound with the leaflets arranged along a rachis to resemble a feather). If a frond is pinnate, the segments of the blade are called pinnae (singular: pinna) and the stalks bearing the pinnae are called petiolules (The main vein or mid-rib of a pinna is sometimes called a costa (pl., costae).

If a frond is divided into pinnae, the frond is called once pinnate. In some fronds the pinna are further divided into segments, creating a bipinnate frond. The segments into which each pinna are divided are called pinnules. Rarely, a frond may even be tripinnate, in which case the pinnule divisions are known as ultimate segments.

Pinnae may be arranged along the rachis either directly opposite one another or alternating up the stem. The arrangement may change from the base of a blade to the tip, as in the example of Blechnum shown below (from base to tip: pinnae opposite to alternate, and pinnatisect to pinnatifid).