I believe there are a couple of types of stammering, but not very many. The most common is developmental stammering which appears in childhood. That doesn't mean that you need to have had obvious dysfluencies, people can also stammer "covertly" by accommodating for their speech with strategies like substituting words, and then these can eventually break down so you develop actual dysfluencies. I am not an expert, but this is what happened to me to the best of my understanding. You can also develop stammering in other ways such as a neurogenic stammering from something like a stroke of traumatic brain injury, sometimes from a traumatic event. Beyond that, as far as I know there isn't much distinctions among diagnoses, its just called stuttering or stammering. I'm used to calling it stuttering, but only because that's more common in the UK. The two terms are generally interchangeable. Stuttering can result in different types of dysfluencies, like repetitions "d-d-d-d-dog", elongations "mmmmmmonkey" and blocks which are periods of silence while trying to speak. (The film The Kings Speech has a lot of examples of blocks.) You can also have chest tightness other symptoms but thats the short of it. I hope that helps!