Comma splice
A comma splice occurs when a writer uses a comma to separate clauses that could stand alone:
My stomach hurts, I'd better not eat any more pasta.
Problem and cure: The comma in this sentence is too "weak" because it separates two independent clauses (or complete sentences). A period should follow "hurts." If the writer wants to show a close connection between the two clauses or "thoughts," she might choose to insert a semi-colon (;) instead. A third possible way of uniting two independent clauses is to link them with a comma and a conjunction:
My stomach hurts, so I'd better not eat any more pasta.
For many writing instructors, the comma splice is one of the more serious usage errors, but it is a relatively easy error to understand and correct.