Hi! c:
stimming is repetitive movements like pacing, fiddling with things, flapping your hands, and so on. There’s a lot of ways to stim, so in most cases if you’re wondering if it’s a stim, it probably is.
for me, i have the choice between being verbal and nonverbal, with my nonverbal times being when i really don’t want to communicate verbally. other autistics have described not being able to get the words out of their throat, or not being able to do all the things necessary for verbal speech at the same time(noises, lip/tongue movements, etc).
I hope this helps you! ^^