Monophony--a musical texture involving a single melodic line and nothing else, as in plainchant.
Polyphony--a musical texture in which two or more distinct melodic lines are played or sung simultaneously. An experienced listener can hear these lines as discrete melodies that harmonize. Each of the individual parts is called a "voice," even when the polyphonic work is performed on instruments.
Homophony--a musical texture that involves only one melody of real interest, combined with chords or other subsidiary sounds that act as accompaniment, as in a typical Bach chorale.
Consonance--intervals or chords that are perceived to be stable and free of tension.
Dissonance--intervals or chords that are perceived to be unstable and tense. Traditionally, a composer "resolves" a dissonance by following it with a consonance.
Point of imitation--in a polyphonic work, a section in which each voice begins with the same or a similar melody (called a "subject"), but one at a time, so that the subject seems to be passed from one part to another. A round can be considered a simple example of imitation. Many polyphonic works of the Renaissance consist of a series of such points of imitation, each on a new subject, but often with overlapping, i.e., with one part beginning before the previous one has finished the subject. In such a piece, each new point of imitation begins as the last voices to enter in the preceding point approach conclusion.
Suspension--a tone that was originally consonant, but has become dissonant because the other parts in the polyphonic texture have moved to a different harmony. Normally, a suspension will be resolved by belatedly moving to a pitch that is consonant with the newer harmony, often to the pitch that is just below it in the scale.
Pedal point--a sustained tone, low in pitch, occurring under changing harmonies, both consonant and dissonant, in the upper parts. [In tonal music, pedal points may occur on any scale degree, but the most common are those on the dominant, preparing a climactic return to the tonic, and on the tonic, as the final, summarizing statement of the tonic at the conclusion of a work.
Passing tone--a passing tone is a dissonance that connects two consonant pitches by stepwise motion and normally occurs in a metrically weak position.