Different Drywalls

They all look the same in the end, so you may be confused why there are so many different types of drywall - or oblivious. Never mind that, there are so many different things to call it: sheetrock, wallboard, gypsum wallboard (or its shorter cousins gypsum board and gyp board, and the Notorious GWB). And sometimes they change “board” to “panel”. Those are all the same thing, and some of the variations on it include:
 
Gypsum rock is mined, crushed, baked, mixed with water to make a slurry, poured out between 2 sheets of paper, dried, cut, then shipped to the jobsite. Thus the nickname sheetrock as it literally is rock spread out on a sheet of paper. It is usually ½” thick for residential jobs and 5/8” thick for commercial jobs (which creates a flatter wall surface and offers more sound and/or fire resistance), but also comes in ¼” and 3/8” thicknesses.
It can be curved – thinner panels bend tighter as shown in this flyer by the Gypsum Association – and wetting it or scoring it allows tighter radii (so sometimes moisture-resistant board is used).
​The narrow ends of the drywall panels are tapered slightly so that when you apply the plaster (“mud” and paper tape to cover the joints, that added thickness ends up approximately flush with the main part of the panel.  Don’t ask me why they don’t taper the long sides, too, but that is a clue as to why the recommended practice is to install the panels horizontally on a wall rather than vertically – the staggered horizontal joints are less visible when you look down along the wall, whereas a continuous tall vertical joint will have a very shallow “speed bump” of plaster every four feet. So drywall walls are not flat but they are much flatter than their predecessor, plaster and lathe.  (Flatness and horizontality aren't the same thing, as if you cared).
 
A few of the major types of drywall include:

• Regular - this is fine for any dry interior space.  Almost everyone uses screws to install it, but be sure to do so and not use nails to minimize nail pops.  Drywallers are fun to watch - kind of like roofers, they want everything ready for them and then they cook and burn through the job in a flurry. And sometimes leave a mess. 
• Moisture Resistant (also called green board since that is the color paper they use to distinguish it). It is losing market share to the below better products, as it still crumbles when it gets "wet" as opposed to "moist".
• Purple board (National Gypsums GoldBond XP, or competitor USG Mold Tough)) is moisture resistant but also mold-resistant, and can withstand direct water contact. This is good for all kitchens and baths but also for exterior soffits and porch ceilings. It is fine for wall tile in dry areas, but for tile in showers and tubs you should use cementitious backer board (see below).
• Paperless means the paper facings are replaced with fiberglass facings. This is best for avoiding mold and moisture problems. However, the fiberglass has a subtle texture so a level 5 finish is recommended (full skim coating with plaster) for discriminating customers.
• Fire-Resistant options include Type C and Type X which are used in various combinations to create UL-tested assemblies with ratings that indicate how long it takes a fire to burn through them.
• Acoustic – a denser panel, often make with a series of panels laminated together by a polymer gel that soaks up sound waves. The screws are an acoustic weak point here, and you should consider using resilient channels first (or also) and using acoustic caulk at the perimeter.
• Abuse-resistant – has a higher density, and a fiber mesh on the backside to hold things together upon impact. This isn’t really needed in a normal house. Bear in mind this is only the board / panel: the corners are still metal beads (normally) which are not any stronger but still in the most-likely-to-be-impacted location, so adding corner guards would seem like an obvious thing to consider if you need abuse-resistant drywall.
• Cementitious Backerboard – not actually drywall, but a cement board such as Durock or a fiber/cement panel board Hardiebacker – this is optimal for use anywhere that wall tiles will be applied. Particularly at tile in tubs & showers, we recommend against any drywall product even though the paperless or purple drywall products can be used there. It is an even better practice to trowel on a coating of waterproofing over the cement board in showers. This product cannot really be used in places where it is not covered by tile, because it does not finish smoothly like drywall does.