Like a comma splice, a run-on sentence occurs because of mistakes in punctuation. However, in the case of a run-on sentence the error occurs when full thoughts are combined without any punctuation at all.
A run-on sentence is two or more sentences strung together without any punctuation. This creates a sense of breathlessness in the reader, as he or she has no punctuation clues indicating where to pause. It can also create confusion because punctuation also serves to help a reader understand how certain ideas connect to each other.
You can correct a run-on sentence in much the same way you would a comma splices: correctly apply a variety of punctuation marks, including periods, commas, and semi-colons, to chop the lengthy sentence up into more manageable pieces. Reading the run-on out loud and listening for pauses is one way of identifying where punctuation should be placed. However, studying and understanding proper punctuation rules for the use of end-punctuation (such as periods, question marks, and exclamation marks), and internal punctuation (including commas, semi-colons, colons, and dashes) is a better strategy.