结巴 can be both a verb (to stutter) and a noun (a stutterer, somewhat rude). The more formal/medical term is 口吃 (kǒuchī). Using 结巴 as a noun to describe someone is considered impolite.
mistakes
Note the unusual pronunciation: 结 here is read jiē (1st tone), not jié. This is one of those words where the character takes a special reading.
