Fracking is a shortened term for a form of energy called "high-volume slickwater hydraulic fracturing". 

Drilling for gas by fracturing shale in verical wells is an established practice, but prior to the twenty-first century, caputuring a multitude of unconnected gas bubbles dispersed within horizontal formation was was not economically feasible.  Enter "fracking".

Using this method, a drill bores down until it intersects with the shale, turns sideways, and continues horizontally for up to a mile or more.  Steel pipe, some portions of which are encased by cement, is laid in the borehole.  Explosives are detonated along the horizontal pipe to perforate it and then, under enormous pressure, a slurry of water, sand and chemicals is forced into the rock fracturing it and opening up preexisting fractures, known as joints.  The chemicals, currently undisclosed due to proprietary rights, serve several purposes; most notably, they reduce friction (thus the term slickwater) so that fracking fluid can flow easily.  In addition, the mixture includes acids, rust and scale inhibitors, and pesticides to kill microbes.  Sometimes it includes gelling agents, petroleum distillates, glycol ethers, formaldehyde, and toluene.

And up the borehold flows the gas.  The cocktail of water and chemicals forced into the fractured shale also flows back up.  But not all of it.  Some 40 to 70 percent stays behind in the rubble.

Fracturing deep bedrock is not a gentle process.  Exerting up to 10,000 pounds of pressure pwer square inch, fracking has been compared to smashing a windshield with a baseball bat.  A single fracking operation requires an access road, 2 to 8 million gallons of fresh water, between 10,000 and 40,000 gallons of chemicals, and at least 1,000 diesel truck trips.  Just to give you an idea of what is going on in New York:  between 34,000 and 95,000 wells are envisioned for New York State, with 77,000 likely.