Answer:
Horizontal bar or rail in a chairback. In the context of furniture, the term crossrail refers to a horizontal support beam or rail that is typically found in the backrest or frame of certain types of chairs or sofas. The crossrail reinforces the structure, provides stability, and helps distribute weight evenly across the furniture piece. It is often positioned perpendicular to the seat rails or leg supports and adds strength and durability to the overall construction.