A catalog-entry-like description. A collection of values that apply again and again. Provides behavior across the collection of all things that correspond to its description. For example, your red pickup is a vehicle; it's a thing with its own serial number (called a vehicle identification number), purchase date, color, and odometer reading. The corresponding catalog-entry-like description is vehicle description; it establishes manufacturer, model number, date of manufacture, and available colors; it also is a good place to locate business-related methods like, "how many of these trucks are in good working order?"
Descriptions often include methods like how many are available and calculate total for quantity. Use a plug-in point when it has algorithmically complex behavior and we want the option of plugging in an alternative behavior at times.