For me it means living in reality rather than fantasy. Acknowledge the phenomenon of stuttering, the social and psychological impact it has on you, how others react, how you react, the difficulties you go through. It's acknowledging that no-one is perfect, and that everything is impermanent, so something may be difficult one day and not the next, that there are aspects of the phenomenon which change, for better or worse, whether by work or by happenstance. If you don't like how things are now, acknowledge completely how things are now, and consider what you can deliberately change to improve things, which in itself can shift as your perspective changes. What acceptance is not, for me, is resignation that nothing can get better. Have the serenity to accept the things you cannot change, the courage to change the things you can, and the wisdom to know the difference.