To illustrate Justme's answer:
Discrete Cosine Transform (DCT) is a lossy
The DCT can't be a lossy algorithm, since there's an inverse operation that restores the original input exactly.
data compression algorithm
Also, it's not a compression algorithm: in- and output have the same size.
So, both your central statements are wrong :(
that is used in many compressed image and video formats,
including JPEG, MJPEG, DV and MPEG.
What's DV? And: MPEG is a huge family of video compression methods. There's not "the MPEG algorithm", there's dozens of different video compression standards under that name.
In this algorithm, special DCT coefficients are calculated for each 8x8 image block.
That applies to JPEG, and probably a few of the many MPEG codecs. It's not true for all MPEG compressors! (For example, MPEG-H Part II, also called H.265, uses blocks of 64×64, 32×32, or 16×16, 8×8 or 4×4, depending on the image content.)
Then the coefficients are quantized
And that's where the lossiness happens: it's not in the DCT, it's what happens to the output of it!
and the image block is represented as a matrix of these quantized coefficients.
Again, only applies to JPEG. Be clear about that!
The matrix is how it's often visualized. The matrix representation is actually non-existent in the memory or storage formats, usually. On the very contrary, the elements are typically stored in a zigzag diagonal ordering if we imagine the matrix. (that's because that puts values that tend to be correlated closer to each other, making the result better to compress using subsequently applied lossless methods like LZW, Huffmann.)
The algorithm utilizes the fact that human visual system does not distinguish small changes in color or intensity.
No, it uses the fact that human perception often cares about high-frequency changes less than about small changes in low-frequency components. Otherwise, the selective quantization would make no sense.
Hm, you've not written the greatest paragraph. But I think you understand a lot of things correctly. Be more careful in really being aware what exactly does what, and you'll be fine!