"Xenomorph" as a term might have got it's actual start in "Alien" but it's commonly used in ScFi references now for any sort of alien that has or can assume multiple forms.
The Alien queens were the real breeders but the face huggers were able to reproduce warrior drones as well. I don't know if it was ever made clear if a face hugger could produce a queen.
All through the first alien film I kept thinking, "This is a dead end species, it has a maximum of one birth per death." (egg to face hugger to warrior). That means every time one is killed they are one step closer to extinction.
My thought during the first Alien film was that they must be artificially created but the sequels introduced the queens and the last film showed their real adaptability with the human-alien hybrid--which was itself and attempt to bump up it's reproductive capability.
It still leaves hte question, "Are the Aliens a created species?".
I'm wondering if Prometheus will reveal the actual origin of the Alien species. I think it will.