Rebar — short for reinforcement bar — is the steel bar or mesh embedded in concrete to give it tensile strength. Concrete is strong in compression but weak in tension; rebar carries the tensile forces that would otherwise crack the concrete, making reinforced concrete (RCC) possible.
Modern rebar in India is almost always TMT (Thermo-Mechanically Treated) steel with ribbed surfaces that grip the concrete. It is placed where tension occurs — the bottom of beams, both faces of slabs, the full length of columns — and held in position by stirrups and ties during the concrete pour.
Concrete cover (a layer of concrete over the bars, typically 25–50 mm) protects rebar from corrosion and fire. Rebar is specified by diameter and quantified by weight using the d²/162 kg/m rule, with the cutting length of each bent bar worked out in a bar bending schedule that accounts for hooks and bend deductions.