This document discusses different types of sentences:
1) Complete sentences have a subject and predicate that form a complete thought.
2) Sentence fragments lack a subject-verb relationship or are missing an important part of a verb string, so they cannot stand alone as a sentence.
3) Run-on sentences connect at least two independent clauses with only one or two words instead of making them separate sentences. They can be corrected with punctuation like semicolons or splitting them into separate sentences.