Diaper: Absorbent fabric, usually cotton, wrapped, folded or sewn to fit a baby like underpants to absorb excrement.
Diaper Cover/Wrap: A waterproof or water-resistant pant that is worn over a cloth diaper to form a moisture barrier between the diaper and the clothing. Many diaper wrap styles also hold the diaper in place without the use of pins or other fasteners. Sometimes, a knitted wool diaper cover is called a soaker.
Diaper Doubler/Booster: An absorbent fabric sewn or folded, similar to a long sanitary napkin, and placed down the center of a cloth diaper for added absorbency.
Liner: This is optional. A thin layer of material laid in the diaper, the purpose being that when the baby messes, the liner can be rinsed or disposed of more easily than the whole diaper. A liner can be washable, flushable, or disposable.
All-In-One: The absorbent fabric diaper and the waterproof cover sewn together making a single-unit cloth diaper/diaper cover combo.