A cardigan is a knitted sweater with buttons or a zipper on the front, which sets it apart from regular knitwear.
A cardigan is a very casual knitted top that works well with a t-shirt, giving you a casual look. It’s still possible to wear a cardigan for work and in the office. If you want a business look with a cardigan, you have to wear a shirt and tie as well. It gives a more casual look than a pullover, but a more business minded look than a turtleneck. It’s the golden mean.