A flat leaflike protrusion of a motile cell, such as a migrating skin cell (keratinocyte) or connective tissue fibroblast, that develops in the direction of movement. It contains bundles of actin microfilaments, which polymerize and extend at the leading edge and become cross-linked to form a supportive network to maintain the shape of the lamellipodium. Lamellipodia often form the ‘webbing’ between finger-like filopodia (see filopodium).