Once upon a time it was easy to differentiate between Film and TV production: film was shot on film, TV was shot electronically. SAG looked after the interests of Screen Actors (film) while AFTRA looked after the interests of Television actors. That the two actors unions have merged is indicative of the changes in production technology.
As is noted in an article at Digital Trends, there is almost no difference between the technologies used in both styles of production, so what are the differences? It comes down to two thing, which are really the same thing.