Run-ons and Comma Splices

Definition:
In prescriptive grammar, two independent clauses that have been run together without an appropriate conjunction and/or mark of punctuation between them.

Usage guides commonly identify two kinds of run-on sentences: fused sentences and comma splices.

Four Ways of Correcting Run-on Sentences:

1. Run-on Sentences:
"Adam is a sweet boy he really loves animals."
"Adam is a sweet boy, he really loves animals."

To correct a run-on sentence, make it into two simple sentences. Put a period at the end of the first subject and verb group. Start the second sentence with a capital letter.

- Correct Sentences: "Adam is a sweet boy. He really loves animals."
(Jill Singleton, Writers at Work: The Paragraph. Cambridge Univ. Press, 2005)

2.Sometimes two sentences are very closely related in meaning and full end-stop punctuation may seem too strong. A semicolon can then be used to divide the two sentences. . . .

- Run-on: "It was a beautiful day there was not a cloud in the sky."
- Correct: "It was a beautiful day; there was not a cloud in the sky."
(Phil Pine, Master the SAT 2008. Peterson's, 2007)

3. A run-on sentence can sometimes be prevented by using a comma and joining word (coordinate conjunction) to join sentences together.

- Wrong: "John went to the movies x Sue stayed home."
- Correct: "John went to the movies, and Sue stayed home."
(Christopher Smith et al., How to Prepare for the GED. Barron's, 2004)

4. Another way to correct a run-on sentence is to change the run-on to a complex sentence by placing a subordinating conjunction before one of the clauses:

- Run-on: "I don't play tennis well I have a poor backhand."
- Correct: "I don't play tennis well because I have a poor backhand."
(P. Choy and D.G. Clarke, Basic Grammar and Usage. Cengage, 2005)

http://grammar.about.com/od/rs/g/runonsentenceterm.htm