Casual is a subculture, which is like a group of people who have similar interests and dress in a similar way. It started in the UK in the 1980s and was mostly made up of football fans who liked to dress in a specific way when going to games. They wore sportswear like tracksuits, hoodies, and trainers, but also added designer brands to their outfits like Stone Island and CP Company.
The casual subculture wasn't just about what they were wearing, it was also about the way they acted and the things they did. Being part of this group made people feel like they were part of something bigger and it was a way for them to show their support for their favorite football team.
So to summarize, casual is a subculture of people who dress in a specific way, mostly made up of football fans who wear sportswear and designer brands. It's also about the way they act and the things they do, and it's a way for them to show their support for their team.