What exactly is a compare and contrast essay?

When required to write an essay as an assignment, the teacher may ask you specifically to write a compare and contrast essay. Or, instead, choosing this particular essay structure may be your own choice. Anyway, it is convenient to know what are you exactly supposed to write about.
Compare and contrast essays are not hard to prepare. This kind of essay is characterized by a basis for comparison, developed in different point or sequences, and analogies, always between two (or sometimes more) terms.