How many series of Friends were there?

In American terms, Friends only had one series because we consider a series the show as a whole. There was a spinoff of Friends called Joey, but it didn't do very well, and I don't know whether or not you want to consider that another series of Friends. I believe that in British terms, a series is one "year," per se, of a show, or what Americans call a season. There were 10 seasons, or series in UK terms, of Friends.