when to use "wait" and when "busy" mouse cursor

I am developing a desktop application with Qt framework. When there is a task running which causes the UI to be blocked for a while, I would like to use a mouse cursor indicating that the user should wait until the task is finished. There are two cursors available - "wait" cursor and "busy" cursor. What is the difference from the UX perspective. What are the rules when to use one or the other?