Rebar, also known as reinforcement steel and reinforcing steel, is a steel bar or mesh of steel wires used in reinforced concrete and masonry structures to strengthen and hold the concrete in tension. To improve the quality of the bond with the concrete,thesurface of rebar is often patterned. Rebar is necessary to compensate for the fact that whilst concrete is strong in compression, it is relatively weak in tension. By casting rebar into concrete, it is able to carry tensile loads and so increase overall strength.