Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has weak tensile strength . Rebar significantly increases the tensile strength of the structure. Rebar’s surface is often “deformed” with ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage.