This term refers to a particular writing style that is imprecise. It leaves the reader with the task of doing all the heavy work of thinking. Or, even worse, it leaves things up to the reader's imagination to try and guess what other things the author might be referring to.

Authors often create run-on expressions when they're giving examples or providing lists of possibilities.

For example, you may already have read the phrase "and so on and so forth." You may have read a sentence that ends with a trailing "etc."

Using this technique in formal academic and professional writing comes off as being "lazy" and lacking in substance.