Nappy Systems
Prefolds
Modern version of flat cloth nappies, made out of cotton with an extra layer in the wet zone and absorb more. You use a cover with these and a stay-dry liner if you want.
Fitteds
A nappy which has snaps or velcro and is shaped so that it is super easy to put on. Some are 'pocket fitteds' which just means it has a pocket so that you can add extra absorbancy if needed. Some have stay-dry liners and some don't. You need a cover with these. And can use boosters - which are usually absorbant material with a stay-dry top.
Pockets
These are a waterproof outer shell and a stay-dry inner which has an opening so that you can stuff absorbant stuff in them (inserts).
All-in-ones
These are everything in one - waterproof shell, stay-dry inner and absorbant material sewn in. Easy peasy but take a bit longer to dry as you can't separate the layers. Some have pockets so you can add extra absorbancy.
Covers
So covers are used with fitteds/flats/prefolds... and I have gone through a stage of using them over pockets at night to prevent anything escaping. They are waterproof (or mostly waterproof) and made from fabrics like Wool, PUL, or fleece.
Fabrics (Not an exhaustive list - I'm learning!)
Cotton
Used as the absorbant part in nappies and comes in forms such as Burley Knit Terry (the most absorbant kind I think) and Sherpa (I think..?). Errrmmmm... I'll add to this as I learn more. Can sit against babies skin, but will feel wet.
Microfibre
Used as the absorbant part in nappies. Soaks up fast but also acts like a sponge so can sometimes 'let go' of the moisture. Fast drying. Can't sit against baby's skin, as it draws moisture too much.
Hemp
Used as the absorbant part in nappies. Soaks up slowly but heaps of liquid and locks it in. The more it gets washed the better it gets.
Bamboo
Used as the absorbant part in nappies. Soaks up heaps of liquid and locks it in. Generally softer than hemp but takes quite a bit longer to dry.
Microfleece
Stay-dry fabric. Wicks moisture through but remains dry on top.
Suede Cloth
Stay-dry fabric. Wicks moisture through but remains dry on top. Less stretch than microfleece.
Cotton Velour
Sometimes used on top of microfleece in nappies. Stay-dry??? Soft as anything and often put on the outside of nappies to make them super cuddly.
Polyurethane Laminate (PUL)
Used in covers/pockets/all-in-ones. Waterproof fabric, with a bit of stretch. There are variations on this fabric but I don't know much about them. Will update when I do
Wool
Natural fibre used as waterproof outer. Keeps warm when cold and cold when warm.
Fleece
Don't know much about this but I'm pretty sure it is polarfleece used in the covers. Will update as I learn more!
Hope that helps