It is amazing how many times I have seen people post the question "What is the difference in stuttering and stammering" and the answer given is often like this one which is NOT correct! There is absolutely no difference; the term stuttering is used in the US and the term stammering is used in the UK.
"Stammering is like when you pause a lot and say 'um' or 'uh' and maybe repeat a word or phrase over and over 'I don't- I don't- I don't know.'
St- st- t- t- t- uttering is when you repeat a short sound over and over when you're trying to get a word out. It can also be a prolonged sound like 'H- hoooo- ow are you?'"
The descriptions of speech in the answer above are just two types of stuttering. A block, where no sound comes out, is also a form of stuttering. Those who stutter stutter a little differently, maybe on different consonants, maybe only on words that start with a vowel, or something else.