A RUN-ON SENTENCE (sometimes called a "fused sentence") has at least two parts, either one of which can stand by itself (in other words, two independent clauses), but the two parts have been smooshed together instead of being properly connected. Review, also, the section which describes Things That Can Happen Between Two Independent Clauses.
Here is an example "I love to write papers I would write one every day if I had the time!" The run on sentence would be... "I love to write papers. I would write one every day if I had the time!"
Hope this helps!!