Prolix means using far more words than necessary to say something. When writing or speaking is prolix, it wanders through unnecessary details, repeats itself, and takes forever to reach the point. A prolix explanation of how to make a sandwich might include the complete history of bread, detailed descriptions of every ingredient's journey from farm to table, and lengthy reflections on the philosophical meaning of lunch.

Think of the difference between “I'm hungry” and “I find myself experiencing a notable sensation of emptiness in my stomach, which leads me to conclude that my body requires nutritional sustenance at this particular moment in time.” The second version is comically prolix.

Teachers sometimes mark student papers with comments like “wordy” or “be more concise” when the writing becomes prolix. A book report that should be two pages but stretches to six pages by repeating the same observations in slightly different ways is prolix. The opposite would be concise writing that communicates clearly using exactly the words needed and no more.

Being prolix wastes your reader's time and can obscure your actual meaning under piles of unnecessary language.