Musical texture is a term used to describe the vertical aspects (layering) of a work or passage.
There are three basic musical textures: monophony, polyphony, and homophony.
Monophony is a single line of music without any harmonic or melodic counterpoint.
Monophony is considered the oldest type of music originating from Ancient Greece and early church music (i.e. plainchant/Gregorian chant).
Figure 1: Monophony: a single line of music.
Polyphony describes music with two or more unique voices played simultaneously.
Figure 2: Polyphony: two lines of music played against each other.
Homophony describes a single melodic line with other parts acting as accompaniment.
Figure 3: Homophony over four staves.
Also see Voice | Counterpoint.