The word yasht derives from Avestan yešti, "for venerate" (see Christian Bartholomae`s Altiranisches wörterbuch, section 1298), and several hymns of the Yasna liturgy that "venerate by praise" are—in tradition—also nominally called yashts. These "hidden" Yashts are: the Barsom Yasht (Yasna 2), another Hom Yasht in Yasna 9-11, the Bhagan Yasht of Yasna 19-21, a hymn to Ashi in Yasna 52, another Sarosh Yasht in Yasna 57, the praise of the (hypostasis of) "prayer" in Yasna 58, and a hymn to the Ahurani in Yasna 68. Since these are a part of the primary litury, they do not count among the twenty-one hymns of the Yasht collection.
All the hymns of the Yasht collection "are written in what appears to be prose, but which, for a large part, may originally have been a (basically) eight-syllable verse, oscillating between four and thirteen syllables, and most often between seven and nine."
The twenty-one yashts of the collection (notes follow):