What they are
The Ten Wings (十翼, shí yì) are the ancient commentaries added to the Zhouyi, the core text. Together they make up the Yijing. They're called wings because they carry the old text further, giving it a moral, cosmological and practical reading.
The ten
There are seven texts, and three of them come in two parts, which makes ten:
- The Tuan, in two parts, on the judgment.
- The commentaries on the images, in two parts: the image of each hexagram and the Small Image of each line.
- The Great Commentary (繫辭, Xici), in two parts: an essay on what the book is, on change, and on the stalk method.
- The Wenyan, only for Activity and Passivity.
- Discussion of the Trigrams (說卦), with each trigram's images, family role and direction.
- The Sequence of the Hexagrams (序卦), on why each one follows the last.
- The Mixed Hexagrams (雜卦), one-line definitions in pairs.
Who wrote them
Tradition gives them to Confucius. Scholars see several hands and generally date them from the Warring States period to the early Han (roughly the 4th to 2nd centuries BCE), centuries after the core text. See Confucius and the Yijing.
In a reading
The Wings aren't the oracle, but they help you read it. When you read a hexagram's image, you're already reading one of the Wings. More in The Ten Wings.