For example, 12 can be the attribute value for the size (in ounces) of a product as well as the value for the number of packing units for a product. attribute: In general, an attribute is a property or characteristic. Whether real-life or fictional, attributes abound for many of us. Let's look at the example … The id attribute specifies a unique id for an HTML element; the id value must be unique within the HTML document. usemap="#planetmap">,