The terms RELEASE NUMBER and BUILD NUMBER can refer to the same thing, the difference is equivalent to model planes built to test how well they fly.

The first plane you build (BUILD NUMBER 0.1) looks good but has all the aerodynamics of a crowbar. You let others play with it anyway, because some of your friends build planes too, and they can suggest ways to improve on your first build.

You decide to improve it after you talk to your friends, so you take it apart look at where you can improve it, and figure if you take out the really stylish brick it might fly better. rebuild the plane (BUILD NUMBER 1.0 big jump in the numbers means a major change, and normally when the numbers go from one side of the decimal to the other means you think it is ready for anyone to use. RELEASE NUMBER 1.0 your figure it is ready to go) So you show your plane to every one and all your plane building friends think it flies like a dream, the problem, anyone else who tries to fly the thing, crashes and burns.

So you talk to the guys who tried it and find out that ones who crashed and burned overfilled the gas tank. So you redesign the tank so that nobody can overfill it. (BUILD NUMBER 1.1 minor change) Nobody who didn't have problems need worry about the change but some of them might try it anyway after all it has got to be better right, bigger number after all.

You go along for awhile and have a really great idea of adding stickers to the plane to make it even better (BUILD NUMBER 1.1.0.1 very minor change)

You get the next great idea bigger engine, swept back wings (BUILD NUMBER 2.1 major change, included a minor change that nobody else got to see because the thing crashed and burned on you, figured if you add wheels it would make it easier to land, minor change compared to engine and wings right) RELEASE NUMBER 2.1 And again you let every one try it, some come back saying I liked the prop and bi plane wings I,m going back to 1.1.0.1 some will say this is great, can we have more and we want different stickers too. So you are on your way to the next build and release, version numbers.

What it works out to be is,

BUILD numbers are all the different versions that are seen by the engineers (ALPHA TESTERS) or software testers (BETA TESTERS) and allows them to figure out what problems the guys see and what the suggestions to fix them are and which versions have what fixes in them.

RELEASE numbers are what the guys figure are suitable for the general public to use with out hurting anything too severely, they can be wrong and if the company is good it will quickly fix the problem and issue a new release.

Some companies just issue the thing as if it is a release version and let all the complaints from the users be their guide in where they went wrong, although that doesn't mean they will fix it, they will just issue a new release and say that, that was were you wanted to be anyway. This way the BETA testers get to pay for the privilege of crashing their systems.