What does maternal depression referrers to?

I’m doing research on the topic of “maternal depression” but I need clarification on something:some places defined maternal depression in four areas–prenatal depression; baby blues; postpartum depression and postpartum psychosis. Other places defined maternal depression as type of depression that comes after postpartum depression. In other words if postpartume depression last more than usual then it becomes maternal depression.
I want to know if the term maternal depression is used to define the four types of depression mentioned above or does maternal depression comes after postpartum depression?

Always go by what the most credible and most cited source defines a term as. In this case, you should look it up on the mayo clinic website or the World Health Organization website.