We will never get everybody to agree on fixed definitions but this is a starting point!
All in one (AIO) – the most similar you can get to a disposable nappy. Everything is sewn together in one piece. Some parts may flap out to aid drying time but nothing will come loose in the wash unless you choose to add boosters. Note: some use the term to mean any nappy that doesn’t require a cover (see ‘one part nappies’).
All in two (AI2) – fairly similar to All in ones as they go on in one piece but have inserts (absorbent parts) that fasten into the nappy, usually with poppers. This makes them quicker to dry than an all in one. You can often buy spare inserts if you find they take longer to dry than the outer. Also referred to as a Snap-in-one (SIO).
Aplix – a type of hook and loop fastening, often referred to as ‘Velcro’ which is a brand name.
Birth To Potty (BTP) – see One Size.
Boosters – come as standard with some nappies or can be bought separately but are generally optional. You would use one/them to ‘boost’ the absorbency if needed. See also Inserts.
Cover/Wrap/Outer – the waterproof part of a two part nappy system, which makes the nappy leak-proof. Covers are often made of polyurethane-laminate (PUL) or thermoplastic polyurethane (TPU) but polyester fleece and wool options are also available. Sometimes ‘outer’ or ‘cover’ is used for the waterproof part of an all in two or pocket nappy.
Fitted nappy (sometimes called shaped nappies) – shaped to fit the baby with elastic at the legs and waist but they are not waterproof so you would normally use a cover over the top. They are the workhorse of the cloth nappy world, often proving to be the most reliable and absorbent nappies for all ages of baby and toddler.
Flat nappy – any nappy that is not shaped and needs a cover to be waterproof e.g. prefolds and terry squares. Often perceived as difficult to use and old fashioned, terries and prefolds remain popular among those looking for reliability at a great price. The learning curve may be steeper at the beginning but once you know, you know!
Front snaps – poppers on the front of the nappy to fasten it.
Hook and loop – a type of fastening, often referred to as ‘Velcro’ which is a brand name.
Hybrid nappy – a cross between two types of nappy. The first hybrids were nappies consisting of a waterproof outer and inserts that are laid into it, with a disposable insert option (so a hybrid between a cloth and disposable nappy). More recently, ‘hybrid fitteds’ have become popular. These are fitted nappies with a water-resistant layer like polyester fleece just inside the outer, making them a cross between a fitted nappy and an all in one.
Inserts – inserts and boosters come as standard with some types of nappy but extras can be purchased to improve absorbency or so you have spares. Generally, if a nappy comes with both an insert and a booster, you will need to use the insert but the booster is optional – you would use it to ‘boost’ the absorbency if needed.
Liner – a non-absorbent layer used next to baby's skin to help catch poo. Washable options include polyester fleece and suedecloth, both of which will help to keep baby feeling dry. Disposable options include paper, cornstarch, viscose and bamboo - these will not do much to help with dampness, they just catch the poo. Disposable liners should not be flushed even if they are described as flushable by the manufacturer - water companies spend a lot of money scooping them out and sending them to landfill because they do not break down like toilet paper.
Modern cloth nappies (MCNs) – generally refers to nappies that don’t need a separate cover to distinguish them from more traditional types. The term is more commonly used in Australia.
Nappy Nippa (Nippa) – a rubber gadget with hooks to hold nappies without fasteners closed. Also known as a Snappi.
Newborn nappy – a nappy sized especially for the newborn period, often fitting from around 5/6/7lbs up to around 12lbs, although brands vary.
One part nappies/one parters – nappies that go on baby in one piece and don’t require a separate cover. Note: some people use the term ‘all in one’ interchangeably with one part nappies.
One Size (OS) (aka Birth To Potty, One Size Fits All, One Size Fits Most) – a term used to describe a nappy that adjusts to different sizes. Most will not fit a newborn baby very well for the first 4-8 weeks, even if the baby falls into the weight range for the nappy, because newborns are often slimmer than older babies of the same weight.
Outer – see Cover.
Pocket nappy – a type of waterproof cover with a pocket in it. You place an absorbent insert into the pocket and then the nappy goes on in one piece. They are a good compromise between the ease of use of an all in one nappy and the quicker drying time of nappies with inserts.
Polyurethane laminate (PUL) – a breathable waterproof layer used in many covers/one part nappies.
Pop-in – a brand name, but sometimes used to refer to all in twos in general.
Prefold – a traditional flat nappy, usually made of cotton, popular in the USA. Rectangular in shape, can be simply folded in three and placed inside a cover, or can be folded around the baby and secured with a Nappy Nippa.
Real Nappy Week (RNW, also referred to as Reusable Nappy Week by some) – a week dedicated to celebrating real nappies!
Shaped nappy – see Fitted nappy
Side snaps – poppers to fasten the nappy that are located at the side of the nappy rather than on the front. These offer a nice flat front and great adjustability.
Sized – a nappy that comes in multiple sizes to see a child through to potty training. Some nappies come in two different sizes, others may come in five sizes (but you may not need all of them as it depends on your baby's weight and build).
Snap-in-one (SIO) – see All in two.
Snappi – see Nappy Nippa.
Snaps (or KAM Snaps) – poppers, often used to fasten a nappy and/or to adjust the size.
Terry nappy – a traditional flat nappy, often made of cotton but newer fabrics are available. Folded and secured around the baby with a Nappy Nippa.
Thermoplastic polyurethane (TPU) – a breathable waterproof layer used in some covers/one part nappies.
Two part nappies/two parters – nappies where the absorbent part and the waterproof part go on the baby separately e.g. terry nappy and cover, fitted nappy and cover.
Velcro – a type of hook and loop fastening
WAHM/Work At Home Mum – (nappy) makers who work at home while caring for children.
Wrap – see Cover.