A run on sentence could be one that goes on and on and never seems to stop. It is usually separated by comas. I have seen this a lot in Spanish text and tis may be fine but not in English. (I might be wrong on this and stand to be corrected)

Una "run on sentence" es una frase muy mal construida porque trata de expresar demasiadas ideas a través de demasiadas palabras sin puntuación o con insuficiente puntuación que es difícil de entender porque es muy larga y complicada, si me explico bien, espero que sí porque he tratado de explicar la idea de una forma muy clara para todas las personas que leen mis palabras que les ofrezco con todo respeto, gracias por su atención.

A run-on sentence is made up of at least two independent parts and each can stand by itself, without losing any meaning. Yes, they are bad. "We got ready for shopping, Eliza couldn't come." You could separate these two into two sentences and not lose any meaning. If we insert 'but' into it, then it is no longer a run-on sentence: "We got ready for shopping, but Eliza couldn't come." You can see that "But Eliza couldn't come." does not have any meaning by itself. Just think - are the ideas expressed in the sentence complete by themselves? If they are, then the sentence is probably a run-on sentence. Look here for more information: http://www.myenglishteacher.net/runonsentences.html