texture

We can characterise texture in time-frequency: on the one hand all parts together in time and frequency (almost together except for octave doubling), at the other extreme are parts independent in time and frequency: Penderecki, Xenakis, (and Ben-Tal :).

Between those extremes we have:

• •  (mostly) homophonic texture - parts together in time but not in pitch.

• Heterephony - parts together in pitch but not in time

• A strict canon is a fixed time shift. This is the simplest kind of canonic device involving transformations in time and/or frequency (Tallis uses both a simple canon in the sopranos but mensuration canon and inversion in the lower voices). Though these relationship are not always audible.

• Commonly, one of the parts is more prominent then the others: the melody. Often as the highest line but not always. 

• It is also possible to consider layers (each one may have more then one part). Ives' Central Park in the Dark or his 4th symphony.   

This video overview about textures (from T. Goss) offers very useful insights