What do you mean? It is all English.
Actually it is. If you're inclined to have your eyes glaze over, just read the last paragraph.
A zbuff is shorthand for Z axis buffer. The depth buffer. Look around you where you are. Your monitor is overlapping the wall, and your table overlaps the floor. Now stand up and back up ... you see how what you see changes as you move. That's what the Z buffer does in a 3d scene generated digitally. Without it everything looks like a flat jumble of stuff and you would never be able to tell what is in front of what.
A programmer can use the Z axis buffer to save on the amount of memory your computer needs to use to draw the game on the screen by not rendering objects that you couldn't possibly see, like when they're behind a wall or a closed doorway, or too distant. That part of the program though had better be efficient if that door opens and the player enters the room, or it'll look weird for a bit.
There's also something called a collision surface, which should keep you from falling through things like walls, floors, elevators, your ship etc. (There is at least one misplaced collision surface in SC, in Area 18. As you enter the tram going to the spaceport, there is a wall like surface blocking part of the doorway. That's the collision surface of the door you just saw move to the right to allow you to enter the tram. but you have to move slightly left to get past it)
A collision surface is something that's only available to a computer program - it's a usually invisible 2D surface that presents a solid barrier to the player he can't pass through. They're used when the player is interacting with a moving object, a sliding door for example, or the floor and walls of your ship. (another example: There seems to be an occasional desynchronization between the interior surfaces of your ship and the collision surface, hence people fall through and find themselves in space. )
These are a couple of very basic things, every developer writing a 3d program needs to know about, and know how to use. That's part of the reason I said this is not about "It's Alpha". This is stuff that should be found in unit testing, that's developer testing their own software to make sure it works as intended and that there aren't holes in the logic. It is, it turns out, one of the hardest things to get developers to do - but it's one of the most important things they can do. Implied timeline: An Alpha is what you (hope to) have
after everything has passed unit testing.