Fragments, Run-ons & Comma Splices
A fragment is an incomplete sentence missing a subject, a verb, or a complete thought; a run-on fuses two independent clauses with no punctuation; a comma splice joins them with only a comma.
Watch for fragments that begin with because, although, or which — they feel sentence-like but depend on something else. Length is no test: a long fragment is still a fragment and a short run-on is still a run-on.