A Cieln (シェルン, sherun?), miswritten as CIEL_N in the localized version of Ar nosurge: Ode to an Unborn Star, is a special type of Song Magic used in the Surge Concerto series that allows to make use of the facilities and functions of the Colony Ship Soreil. It could be said that they are equivalent to the Hymmnos Extracts from the Ar tonelico series.
These songs are programmed into the Surge Concerto Terminal rather that being crafted by a Weaver or Genom within their Soulspace, so they must be Downloaded into the singer's mind in order for them to be able to use their powers. However, since the Download requires a considerable amount of time, the person performing the Download and the singer must find a place where they can conduct it in peace, as any agitation could disrupt the process, either damaging the feelings comprising the Cieln, or even canceling the Download altogether.
As the Cielns are based off the ClassDrive programs that existed back during the Ra Ciela days, and the Surge Concerto Terminal itself is also partially based on these old systems, these songs share the same naming format as the ClassDrive programs: Class::XXXX;