YUV is the common, quicker way to type Y'CbCr which is this colourspace:
http://en.wikipedia.org/wiki/Y%27CbCr
4:2:0 is the chroma sub-sampling used:
http://en.wikipedia.org/wiki/Chroma_subsampling
8-bit means how many bits per sample are used, almost:
http://en.wikipedia.org/wiki/Color_depth
As for what happens when you load this file into your program, who knows? It is compressed, so you could be reading it without decoding; or reading the output of the decoder which should as mediainfo describes the file in which case it is more likely to be 16-235 luma and 16-240 chroma; or it has been converted to RGB for display in which case it is likely to be 0-255.