Developed in the late 1940s, fracture stimulation, also known as hydraulic fracturing, is the practice of injecting a well with large amounts of frac fluids under high pressure in order to break the rocks.

Fracture stimulation improves hydrocarbon flow by creating fractures in the formation that connect the reservoir and wellbore.

Fracture stimulation can increase the production of a well by 1.5 to 30 times the initial rate of flow, as well as the overall production from 5 to 15%. Also, a well can be fraced multiple times during its production life. Sources: http://www.rigzone.com/training/insight.asp?insight_id=319
https://www.cred.org/explore/what-is-fracking