Does anyone know what Iberia Singular is? The boarding gate screens during the call for priority boarding always show Singular in addition to Plata, Oro and Platinum.

A quick google search shows the FAQ of Iberia.com (where it is not answered) and a few random pages that say it is by invitation only. The Iberia website also mentions it a few times, but does not explain what it is.

Is it the equivalent of the BAEC Premier, and only given out to people who control large travel budgets? Or is it something given to friends and family of Iberia staff?