In general, appearance would be the visual characteristics of the item in question (example water is a colorless liquid), while description can be much more involved and detailed (water is dihydrogen oxide at room temperature. In its pure state, it is odorless, colorless and tasteless, with a specific gravity of 1.0 Freezing point is 0° Celsius, boiling point is 100° Celsius.) As you can see, a description is a much more precise way of identifying something.