Final answer:
The broad, flattened, veil-like protrusion extended out from a fibroblast cell is called a lamellipodium, which is essential for cell motility.
Step-by-step explanation:
The broad, flattened, veil-like protrusion that extends out from a fibroblast cell is known as a lamellipodium. The lamellipodium is a cellular structure that plays a critical role in cell motility and migration. It is primarily made up of a dendritic actin network that pushes against the plasma membrane to help the cell move. It forms at the leading edge of the fibroblast as it attaches to the extracellular matrix (ECM) via integral membrane proteins called integrins. In addition, the fibroblast secretes various components of the ECM, contributing to the connective tissue structure. The actin-myosin interactions also lead to the formation of contractile actin filament bundles, commonly known as stress fibers, which provide tension and support to the cell's structure.