Keep in mind that "silver" is not a universal term. Precious metals mean different things to different airlines. Some even use non-metallic designators such as "Senator," "Premier" or "Chairman's Preferred." It's like referring to dollars without specifying if you mean the U.S., Australian, Canadian or some other type. Better to say "first-tier," "mid-tier" or "top-tier" elite, though even this falls down with airlines that don't use three tiers.