( ( ( ( ( fracking , ) or ) hydraulic ) ( ( fracturing ( ( The ( cracking open ) ) ( of ( undergound rocks ) ) ) ) ( by ( ( ( ( introducing liquid ) ( at ( high pressure ) ) ) , ) ( especially ( to ( extract ( natural gas ) ) ) ) ) ) ) ) . )
(ROOT (S (S (VP (VBG fracking))) (, ,) (CC or) (ADVP (RB hydraulic)) (S (VP (VBG fracturing) (NP (NP (DT The) (JJ cracking) (NN open)) (PP (IN of) (NP (JJ undergound) (NNS rocks)))) (PP (IN by) (S (VP (VBG introducing) (ADJP (JJ liquid)) (PP (IN at) (NP (JJ high) (NN pressure))) (, ,) (S (ADVP (RB especially)) (VP (TO to) (VP (VB extract) (NP (JJ natural) (NN gas)))))))))) (. .)))
fracking, or hydraulic fracturing  The cracking open of undergound rocks by introducing liquid at high pressure, especially to extract natural gas.
(ROOT (S (NP (NNP Fracking)) (VP (VBZ is) (NP (NP (DT another) (NN term)) (PP (IN for) (NP (JJ hydraulic) (NN fracturing))))) (. .)))