Renewable energy is useful energy that is collected from renewable resources, which are naturally replenished on a human timescale, including carbon neutral sources like sunlight, wind, rain, tides, waves, and geothermal heat. This type of energy source stands in contrast to fossil fuels, which are being used far more quickly than they are being replenished.

Re-rollable scrap is a steel scrap metal that is already in such a condition that it is suitable for another application through rolling it into a saleable product. This differs from the more common processes seen in scrap recycling where the metal undergoes melting, casting and rolling. Re-rolling is more commonly used in emerging economies rather than in industrialised countries. 

The underground formation where oil and gas has accumulated. It consists of a porous rock to hold the oil or gas, and a cap rock that prevents its escape.

Oil that does not move when fluids are flowed through the rock in normal conditions, for example primary and secondary recovery, and invasion.

Residuals are elements such as copper and tin, which are usually introduced into the steelmaking process in the form of unsorted or contaminated scrap. This can sometimes, however, impair the physical and mechanical properties of steel. Residuals are key concerns regarding the mini-mills’ recent entry into the flat-rolled market. High residuals can leave sheet steel too brittle for customer use causing problems in the mill.

Undesirable elements in the scrap (particularly copper) which are generally harmful to the steel manufacturing process.

A reversible,or regenerative,fuel cell can operate as a fuel cell,or in reverse like an electrolyser.

A reversing mill is used to reduce material to gauge. The steel enters the rolling mill from one side, passes through the other side and then comes back through the mill again. Normally it will go left to right through the mill a number of times being rolled a little thinner each time it goes through.

REX (Range Extenders) is a fuel-based auxiliary power unit (APU) that extends the range of a battery electric vehicle by driving an electric generator that charges the vehicle's battery. This arrangement is known as a series hybrid drivetrain. The most commonly used range extenders are internal combustion engines, but fuel-cells or other engine types can be used.

Natural gas containing heavier hydrocarbons than a lean gas. Its liquid content adds important economic value to developments containing this type of fluid.

Lean oil that has absorbed heavier hydrocarbon components from a gas stream.

A rig is the machine used to drill a wellbore. A rig is either structured on land or sea for it to access oil from the ground. 

This type of steel is produced during ingot casting, with the resulting ingot having a very pure surface layer, or rim. This feature is due to the absence or near absence of a deoxidising agent during steel production, which allows carbon monoxide to be formed from the oxygen and carbon in the melt. As this gas migrates to the surface, other elements (eg.carbon, phosphorus and sulphur) gravitate towards the centre of the ingot to leave a much purer layer or rim on the outside. After hot rolling this steel has a good surface finish which is low in carbon.

Roasting is a process of heating a sulfide ore to a high temperature in presence of air. It is a step of the processing of certain ores. More specifically, roasting is a metallurgical process involving gas–solid reactions at elevated temperatures with the goal of purifying the metal components. Roasting consists of thermal gas–solid reactions, which can include oxidation, reduction, chlorination, sulfation, and pyrohydrolysis. In roasting, the ore or ore concentrate is treated with very hot air. 

A machine which converts semi-finished steel (semis) into finished steel products by passing them through sets of rotating cylinders which squeeze the steel into the desired shape. Rolled steel products include bar, rod, plate, beams, coil etc.