What's the deal with pocket diapers?

What is it?
Pocket diapers are similar to all-in-one (AIO) diapers, and, when stuffed, are essentially the same thing. So what's the difference? And what's stuffing? A pocket diaper has a lining sewn into the waterproof outer, with an opening (or two) left at the front of the diaper, back of the diaper, middle of the diaper, or both, which allows you to put the unattached absorbent layer (the insert) into the diaper.  Before washing, you remove the insert so it washes separately outside the diaper, and before placing it on the baby, you'll need to "stuff" the insert back into the diaper.  The pocket opening and removable inserts allow you to customize the absorbency; for instance, some people will "double stuff" a pocket with two inserts for night, and use just one insert during the daytime.

Some pockets have elastic or  foldover pieces of fabric at the opening to help contain the insert, while others are loose.

Pocket diapers almost always have a stay-dry feeling.

What do they look like?

Happy Heiny pocket diaper showing pocket opening

Happy Heiny pocket diaper with insert halfway removed

Bum Genius microfiber insert shown alone (without pocket diaper)

Oh Katy diaper showing pocket opening in front (hard to see, but on the right side of the picture), with a foldover layer of fabric to protect the opening.

 Rumparooz pocket opening at back

Alva pocket opening, with elastic

Thirsties pocket diaper with elasticized openings at front and back

What size do they come in? How do they close?
These can be sized or one-size and may close with snaps or velcro.

What kind of variations are there?
Sleeve pockets have openings at both ends instead of just one.  This can make it easier to stuff and supposedly allows the insert to agitate out on its own during the wash - but many people unstuff them anyway, just to be sure. And not all washers will agitate out the pocket (HE washers are notorious for leaving them "stuffed".)
Envelope pockets have openings in the middle. Again, this supposedly allows the insert to agitate out on its own in the wash.

What are the pros and cons?
Pros:
Can add or remove inserts to personalize absorbency, can replace included insert with a different kind, dries quickly, inserts get very clean since they are washed separately.

Cons:
Have to stuff and unstuff. Can be bulky. Unstuffing diapers can be difficult with a very poopy diaper.

How do I care for my pocket diapers?
Most pocket diapers are made of synthetic materials, which means to prep your pocket diaper you just need to wash it once.  After the diaper has been prepped, you can wash using your normal cloth diaper wash routine.  Depending on the brand of diaper and type of washing machine you have, you'll likely need to pull out the insert prior to washing. Some people do this immediately after taking the diaper off the baby and some people unstuff just before putting the diaper in the washing machine. Be sure to attach the laundry tabs for velcro diapers. After the diaper is washed and dried, you'll need to re-stuff the insert back into the shell before use. Again, some people do this for all their diapers immediately; others stuff as needed.

What are common brands of pocket diapers?
Bum Genius 4.0
FuzziBunz
Rumparooz
SunBaby
Alva
AppleCheeks
Blueberry
Happy Heiny
Kawaii
Knickernappies