Rebar is short for reinforcing bar, but is most commonly known as reinforcing steel or reinforcement steel. It is a steel bar or a mesh of steel wires used as a tension device in reinforced concrete and masonry structures. Its primary use is to strengthen and hold the concrete in compression. Even though concrete is strong under compression, it has weak tensile strength. Adding rebar to the structure can significantly increase tensile strength and its surface is patterned to form a better bond with the concrete. 

The most common type of rebar supplied is carbon steel which usually consists of hot-rolled bars with deformation patterns. Other types can include stainless steel, and composite sections typically made of glass fiber, carbon fiber, or basalt fiber. However, it is important to note that these alternate types tend to be more expensive or have lesser mechanical properties and are thus more often used in specialty construction where the rebar’s physical characteristics fulfill a specific performance requirement that carbon steel does not provide.