The document defines an analogy as a comparison of concepts based on how they are alike. It provides examples comparing a dog to a puppy and scissors to a broom. Analogies can be of different types including synonyms, antonyms, characteristics, parts/whole, degree, type, tool/worker, action/object, item/purpose, and product/worker. While analogies can enhance writing, the document cautions that not all analogies are effective, providing absurd examples of analogies that do not clearly illustrate similarities.