A cardigan is a type of knitted garment that has an open front. Commonly cardigans have buttons: a garment that is tied is instead considered a robe. A more modern version of the garment has no buttons and hangs open by design. By contrast, a pullover does not open in front but must be "pulled over" the head to be worn. It may be machine- or hand-knitted.
A cardigan cannot be machine-knitted.