What does fracking refer to in the context of energy production?

Fracking, short for hydraulic fracturing, is a method used to extract petroleum and natural gas that are trapped within underground rock formations. The process involves injecting a high-pressure mixture of water, sand, and chemicals into these rock layers, creating fractures that allow the oil or gas to flow more freely to the surface. This technique has become increasingly important in recent years for tapping into reserves that were previously considered inaccessible and has significantly contributed to domestic energy production.

The other choices describe different energy production methods. Mining for coal involves extracting solid fossil fuel from the ground, which is distinctly different from the extraction of liquids like oil or gas. Harvesting solar energy focuses on capturing sunlight using solar panels, a renewable energy source entirely unrelated to fracking. Collecting biofuel involves processing organic waste materials into fuel, which also does not pertain to the method of extracting hydrocarbons from rock formations that defines fracking.