According to TFwiki the term "combiner" is very broad. The article has a fairly comprehensive list of what counts as "Combiners" and even what sub-class of "Combiner" that they fall under. Source.

The article does fail to mention the fact that "gestalt" has now entered official currency though in Animated and IDW. In Animated the term was used to describe Jetfire + Jetstorm = Safeguard, whereas in IDW it was used to describe Devastator (re: AHM).