A definition I like is one from midwife and author, Penfield Chester:

“The holistic model holds that birth is a normal, woman-centered process in which mind and body are one and that, in the vast majority of cases, nature is sufficient to create a healthy pregnancy and birth.”

My certifying organization, ALACE, uses the word holistic to mean a childbirth educator who incorporates psychological aspects and mind-body integration into their classes.