A "run-on" sentence occurs when the writer has blended two or more complete sentences into one, either by using no punctuation or by using only a comma.
These are both run-on sentences:
Here is how you can fix them:
Note: Complete sentences joined only by a comma are sometimes called a "comma splice," which is a type of run-on sentence error. Using a comma by itself is likely to confuse the reader because commas are used in many other situations. (See the section on comma usage.)
To fix run-on sentences: