Attunements are special gifts from a Superior (or rarely, a powerful Ethereal) that allow an individual to affect reality. Unlike Songs, attunements have no level and usually don't have a chance of failure; they work how they work. (Some attunements that are used against a target can be resisted, though.)
Examples of attunements include Laurence's Scabbard attunement, which allows an angel to hide a weapon in "thin air" and pull it out at need, or the Dreamwalking ability granted by both Blandine and Beleth.
In a different context, "attunement" can also refer to the special Choir or Band abilities granted by a Superior, or to the attachment that a Cherub or Djinn has that allows it to follow a target throughout the Symphony.