Definition of run-on sentence:
(n) :
(grammar) A written sentence that inappropriately joins two (or more) independent clauses into a single sentence, often with only a comma as separator (comma splice), which should be rendered either as separate sentences or as clauses joined more appropriately (such as by a semicolon or by a comma and coordinating conjunction).
(n) :
Any very long, often also in other ways badly formed or even chaotic sentence.