Subjective video quality is how you feel about a video or movie. Sometimes people like different things about video quality. Some people might like bright colors or smooth movements, while others might prefer natural tones or realistic effects. It's like when you go to a restaurant - some people might really like the food they get, while others might not like it as much.
To measure subjective video quality, people watch a video and rate how much they like it. They might also tell researchers what they like or don't like about the video. Researchers use this information to improve video quality so that more people like it. So just like how a chef might change some ingredients in a dish to make it taste better, video makers might change parts of a video to make it look better and be more pleasing to people.