"Holistic review" is a relatively meaningless term designed to get low MCAT or low GPA applicants to apply, in my opinion. Individuals that clearly need improvement in one aspect of their application are told that it doesn't matter because they are strong elsewhere. Well, the reality is, there is a very strong maybe that you could get in, but it's absolutely not worth the money and risk. Take this from someone who applied this year and is now working on gearing up for a reapplication, which I can not safely submit until 2018.
It doesn't matter how "holistic" a review process is, they are still going to accept the better applicant - and there are plenty of better applicants in any given pool, especially if you have a low MCAT. Things like having a great MCAT, extensive leadership, lots of clinical work, military background, D1 athletics, etc. are all going to help you everywhere. "Holistic" schools and "non-holistic" schools don't care; if the applicant is strong, they are strong. No "holistic" process is going to help someone with limited ECs get in because they are "looking at the whole person." I interviewed at a school that highly promotes "holistic" review this cycle, you can PM me if you want more details. My 2 cents: it doesn't mean anything, it's a coined term like what DOs have done with "holistic" care. "Holistic" fads need to die.