Joint custody often means that the custody of the children are fairly equal and balanced between the parents. The questions are more about legal custody and physical custody.
Legal custody is almost always joint, which means that it is equal among the parents. The rights and responsibilities for the child, the costs for the child, making major decisions like medical treatments are almost always joint among parents that both want to be part of the child’s life.
Physical custody deals more specifically with the living arrangements: the day-to-day, week-to-week schedule of actual physical care of the child. Physical custody may also be joint and fairly balanced between the parents or less so based on any number of factors.