A khyal is a raga form.

From the CD notes:

Barker based his "raga/row/melody" on the kanakangi scale and the work follows the nine part khyal raga structure.

From Wikipedia:

Khyal (or khayal) is the modern genre of classical singing in North India. Its name comes from an Arabic word meaning "imagination".

On raga from http://indianraga.blogspot.com/2007/09/back-to-basics.html:

Melody is the fountainhead of Indian music and ragas are the fundamental organizing principle of Indian classical melody.

Ragas are fixed sequences of a minimum of five notes, arranged in ascending and descending order (respectively the aroha and avaroha). …like the modes of early European music, the ascending and descending notes are not identical. Adjust the sequence or introduce an extraneous note and the result will be a different raga. …

Ragas unfold in a set order. The opening movement, called alap … a leisurely, precise, impassioned unfolding of the raga's essence. It teases out the mood with melody … without any rhythmic accompaniment or rhythmic pulse.

From notes to a program with Trikhyalo (see image teb39.program_notes.tif):

A khyal is an Indian raga form that traditionally contains nine parts and, although Trikhyalo ("Tri-" connotates the three players) is not improvisatory, its row and overall structure are generated from the Indian model.

The composer's own words:

Trikhyalo is based on a raga from "khyal" common to both northern and southern Indian musical cultures. The raga/row/melody, which contains the fundamental pitch material for the work, is constructed from the kanakangi scale (C Db Ebb F G Ab Bbb c), although it has been modified to create a 12-tone set. The work falls into the traditional nine part khyal structure: a) Alap / rhythmically free prelude which presents essential features of the raga/row/melody; b) Asthayi / emphasizes the notes of the lower tetrachord or, as in my work, a hexachord; c) Anatara / emphasizes second hexachord; d) Alap / elaboration; e) repetition of Asthayi and Antara / entire melody presented; f) Bol-tans / fast passages or variations; g) repetiton of e; h) Tans / virtuoso part - solo section; i) conclusion, either a repetition of the Asthayi or a new section, fast melody.