The term ‘histrionic’ developed from ‘histrion-, histrio,’ Latin for ‘actor.’ Something that is ‘histrionic’ tends to remind one of the high drama of stage and screen and is often ‘over the top’ and stagy. It especially calls to mind the theatrical form known as the ‘melodrama,’ where plot and physical action, not characterization, are emphasized. But something that is ‘histrionic’ isn’t always overdone; it might simply refer to an actor. In that sense, it becomes a synonym of ‘thespian.’
(Of course, it is also a personality disorder.)