(most definitions from http://www.diaperpin.com/)
For the baby with sensitive skin there are also wool and polar fleece diaper covers. These too may be contoured shaped with snap or velcro fasteners. Others come in "boxer-like" shape. Some prefer these covers for night-time use because they breathe.
Inserts: (Pictured are the Knickernappies LoopyDo and microfiber inserts, available at http://www.bumcovereddiapers.com/ and other retailers)
Inserts are the absorbent piece of a pocket diaper and are placed in the "pocket" of a pocket diaper to keep babies dry. Inserts are made of many materials, with the most common being microfiber and hemp.
All-in-one diapers: (Pictured is the bumGenius 3.0 All-in-one (AIO), available at http://www.bumcovereddiapers.com/diapers/all-in-one-diapers.html and other retailers)
Also known as AIO's, all-in-ones are fitted diapers that have an outer waterproof layer and a built-in soaker (insert). These are the diapers closest to disposables, and will probably be the easiest to use for parents who are new to cloth.
Liners: (pictured are Bum Covered Fleece Liners, available at http://www.bumcovereddiapers.com)
Liners are thin material used between a baby's bottom and the diaper itself. Most liners are used to keep stool away from diapers for easy clean up. Many cloth diaper businesses carry flushable biodegradable liners which are the perect fit for this purchase. As an alternative you can use flat diapers to keep costs down and still keep natural soft fabrics against your baby's skin.
Another type of liner which is fast becoming popular is the polar fleece one. These are thicker than their paper/flat sheet counterparts and are great for keeping the baby's bottom dry.