( ( ( ( Alternating Current ) ( -LRB- ( AC -RRB- ) ) ) ( ( An ( electric current ) ) ( that ( ( reverses ( its direction ) ) periodically ) ) ) ) . )
(ROOT (NP (NP (NP (VBG Alternating) (NNS Current)) (PRN (-LRB- -LRB-) (NP (NNP AC)) (-RRB- -RRB-))) (NP (NP (DT An) (JJ electric) (NN current)) (SBAR (WHNP (WDT that)) (S (VP (VBZ reverses) (NP (PRP$ its) (NN direction)) (ADVP (RB periodically)))))) (. .)))
Alternating Current (AC) An electric current that reverses its direction periodically.
(ROOT (S (NP (VBG Alternating) (NN current)) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (JJ electric) (NN current))) (SBAR (WHNP (WDT that)) (S (VP (VBZ keeps) (S (VP (VBG reversing) (NP (NN direction))))))))) (. .)))