Showrunner (alternatively, but not commonly, show runner) is a
term of art originating in the United States television industry referring to the person who is responsible for the day-to-day operation of a television series — although such persons generally are credited as an
executive producer[1] or supervising producer.
...The term "show runner" was created to identify the producer who actually held ultimate management and creative authority for the program. The blog (and book) Crafty Screenwriting defines showrunner as: "...the person responsible for all creative aspects of the show, and responsible only to the network (and production company, if it's not his production company). The boss. Usually a writer."