The broken-off word main- is called a fragment.

University of Michigan - Ann Arbor

An utterance is the spoken correlate of a sentence.

Utterance

An on-going but a helpful book resource about NLP
https://web.stanford.edu/~jurafsky/slp3/

Words like uh and um are called fillers or filled pauses.

A lemma is a set of lexical forms having the same stem, the same major part-of-speech, and the same word sense. 

 The wordform is the full inflected or derived form of the word.