Fracking is the process of injecting high pressure liquid ('fracking fluid') into an underground formation to open up the formation to release trapped oil or gas pockets. Fracking is also referred to as hydraulic fracking, fraccing, frac'ing, hydrofracturing, or hydrofracking. Fracking is completed after the well has been drilled. Fracking is commonly used for shale wells containing oil or gas deposits.
Fracking fluid is primarily water but also contains sand or other proppants. Sand and proppants help keep the formation open while oil or gas is being produced up the wellbore.