What does the letter 'C' represent in steel terms?

In structural steel terminology, the letter 'C' specifically denotes "Channel." A channel is a type of structural steel member with a cross-section shaped like the letter 'C.' It is commonly used in construction due to its strength and versatility, primarily for beams, girders, and braces. Channels provide good load-bearing capabilities while being relatively lightweight compared to other structural shapes. Their design allows for efficient distribution of loads in various construction applications, making them essential in the field of structural engineering and welding.

While other options represent materials or concepts commonly associated with construction—such as carbon (a pivotal element in steelmaking), concrete (a vital construction material), and composite (referring to materials made from two or more constituent materials)—they do not match the specific definition of 'C' in steel terminology. Thus, channel is the correct term that aligns with the context of steel.