Rebar, reinforcing bar, reinforcing steel, and reinforcement steel are all terms for steel reinforcement bar. It is a versatile building material that is widely used in the construction industry to make reinforced concrete. Reinforcement concrete (RC) is a composite material composed of concrete and reinforcement, most commonly steel rods, bars, wires, or a mesh of steel rods and steel wires. Steel reinforcement bars are typically of such shape and size that they can be easily bent and placed in concrete to form a monolithic structure.

Steel rebar is most commonly used as a tensioning device to reinforce concrete in order to keep it compressed. Concrete is a material that is very strong in compression but almost non-existent in tension. To compensate for this imbalance in the behaviour of a concrete slab, reinforcement bar is cast into it to carry tensile loads. To improve the bond between the reinforcement bar and the concrete, the surface of the reinforcement bar can be patterned.