A "hot-rolled coil" (HRC) is also called a "hot-rolled steel sheet". A slab made in a steel production factory is heated in a furnace, rolled-formed continuously and many times into a strip shape with several roll-forming machines, and then wound into a coil and transported.
Hot-rolled coils are made in thicknesses ranging from 1.2 to 14 mm (0.047in to 0.551in). Because hot-rolled coil is being rolled-formed after applying heat, which makes the steel soft and easier to forge, the surface of the coil has an oxidized black residue ("scale") and a black appearance. HRC is used in a wide range of fields such as building materials and industrial machinery materials.
There are various types of steel sheets, such as cold-rolled steel sheets and galvanized steel sheets. Please refer to the link below for more details.
Reference: Strip Steel (Wikipedia)