I don't know the keyword, but I have an idea to create a 3D model in an 8bit style, and I was trying to google everything from "8bit 3D model" to "isometric 3D modeling technique" to "8bit to 3d model conversion".

The idea is to make a 3d model out of extrusions only, in a sort of 8bit style, and rig this 3D model. Then I can animate it from a side view (or other views).

I couldn't find anything that looked like what I wanted. Any suggestions on keywords?

I found something perhaps similar:

Is there a name for this style? I am looking for tutorials.

Update: Came across a keyword "Voxel?"

Okay, in my research I found an awesome piece of free software that will help me explore this style:

https://voxel.codeplex.com

Pixel is a 2d picture element, voxel a 3d volume element. Therefor voxel will give you a superset of what you want to archive. Eg. minecraft is although a voxel game.

A transformation from a sprite to a 3d model like you displayed in your screenshot, is quite easy:

Given is a sprite with width w and height h.

For each visible pixel at position x,y with color c and depth d (you need to add a depth value to the pixels) you need to construct a cuboid with the extension (1,1,d) at position (x,y,0) and color c. That is all, just put all cuboids in a single model and add a proper scale factor and you are done.

Instead of rigging your model you could do the animation in sprite form and transform each frame to a 3d model, but this depends on the art style, number of frames, sprite size etc.

Yup, it looks like voxels to me. You could likely make things work with a traditional rendering engine(as in verts/quads) by building your models out of cubes(and removing the polys from the insides). This assumes you don't want some things specific to voxels in some engines, like destruction, terrain, etc... that requires actual voxels to do.

About animation, I don't think you are going to get bone based animation to work right. Things tend to work based mostly on rotations, and you won't keep the same style if you start rotating all of those little cubes. So, you more likely would need something like Ashaman mentioned above, making each frame as a separate model, and simply rotating between them frame by frame as you would if you were making a sprite based game, going through frames of animation.

Thanks for the tips. I have to look into animation. This will be perfect for my beginners game making tutorial, because it makes the modeling stage a lot easier.

You can still do traditional rotation based matrices for sprite animation if you do it carefully and plan for it.

Basically you preserve a separate skeleton for skeletal animation and rather than rotating the model with the skeleton you render voxels along the skeletal lines using interpolation ensuring that their plane is still horizontal so they don't look strange. This way it has the appearance of classic 2D animation without the need to pre draw dozens of frames. It will take quite some tweaking but in my opinion it would be worth it...