Meaning of extra-base hit

ex'tra-base' hit'

Pronunciation: (ek'stru-bās'), [key]
— Baseball. Baseball.
  1. a base hit that enables a batter to reach more than one base safely, as a two-base hit, three-base hit, or home run.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.