A chordioid, also called chord fragment or fragmentary voicing or partial voicing, is a group of musical notes which does not qualify as a chord under a given chord theory, but still useful to name and reify for other reasons.
The main use of chordioids is to form "legitimate" chords enharmonically in 12TET by adding one or more notes to this base. It is typical of chordioids that many different resultant chords can be created from the same base depending on the note or combination of notes added. The resultant chords on a single chordioid are somewhat related, because they can be progressed between using motion of just one voice. Theorists – or practical music teachers – writing of chordioids usually go so far as to advise that students learn them in the practical manner of chords generally: in all transpositions, ranges, permutations, and voicings, for reading, writing, and playing. It is the case, also, that "legitimate chords" can be used as chordioids to create resultant chords by the same process. Perhaps this is whence the non-chord chordioids come. The Italian augmented 6th chord (It+6) is one example, from which proceed the French augmented 6th chord (Fr+6) and German augmented 6th chord (Gr+6) by addition of one note. Rawlins (2005) asserts that the notion derives from practice of such composers as Eric Satie, Claude Debussy, Maurice Ravel, and Gabriel Faure, and was first used in jazz by Bill Evans.
Two chordioids may potentially be combined, as well. Typically, duplication of notes will result in a reduced number of unique notes in the resultant.
Chordioids as a technique is related to polychords insofar as polychords are the result of an additive process, but differs in that the basis of polychords is the addition of two known chords. Chordioids is related also to upper structures as a technique insofar as upper structures represent groups of notes not commonly taken to be "legitimate" chords, but differs in that chordioids as a technique uses a priori structures held in common rather than a free selection of color tones appropriate for a lower integral chord. Chordioids is related to slash chords as a technique insofar as known chords may be used as chordioids to create resultant scales, but differs in that chordioids used are not exclusively known chords.