The phrase "absorbent part" refers to the section or material that is capable of soaking up or taking in liquids or substances. It can absorb and hold moisture or other substances, like a sponge or a paper towel. Full definition
This will keep the most absorbent part of your prefold in the center of the trifold, as shown here: (cozybums.ca)
These two types are similar, except that pocket diapers have a removable absorbent part where as the AIOs are all sewn together in one piece. (askmoxie.org)
But beyond that, when our feet (the most absorbent parts of the body) make prolonged contact with the Earth, the strong negative charge of the Earth quite literally grounds the positive ions of the body. (solfulhealth.com)