Braxton Hicks contractions are the way in which a woman's body prepares for true labor and the actual birthing process. These "practice" contractions are usually painless, and the cervix does not dilate (as it does with true labor). In most cases, Braxton Hicks contractions ease up with activity or a change in position.
(Click Braxton Hicks Contractions for more information about when Braxton Hicks contractions typically begin and how they differ from true labor contractions.)