It means your video has 8 bit depth per pixel, per channel, Red, Green, and Blue.

Add the fourth channel (Alpha), and it becomes 32 bit video.

Unless you are talking about YUV, then it works a bit differently (doesn't seem like it would be capable of producing as many colors... does anybody know if 4:4:4 YUV can still hit 16.7 million colors as well like 8 bit RGB can? It doesn't seem like giving 8 bits to luma and only using the remaining 16 to describe color information would be able to produce as many discrete colors as RGB.

Even YUV ends up being an RGB value once it gets to the screen, though.

Many things can deliberately reduce actual bpp in YUV encodes; the biggest by far is Interframe Compression, CABAC, b-pyramid, dct, and a few other tricks. Chroma subsampling by itself these days is a rather minor player by comparison.

If you want to test this for yourself, compare file sizes between RGB and Sony YUV, which is not Interframe. Then compare with High Profile h264/x264, which is YUV and Interframe.

Does anyone know, without any compression applied at all, and no chroma subsampling, how many colors YUV 8 bit would be capable of producing? I know uncompressed RGB gives us 16.7 million possible colors. Just trying to get an idea of exactly how many possible colors a camera shooting an uncompressed YUV frame could produce, and how many it loses by not going full range 0-255.