My music theory book best put the definition of texture as "The way melodic, rhythmic, and harmonic are woven together in a composition."
By this definition the texture of a piece is a combination of all the pieces that make up music, but looking at them all together instead of separately. A composer will use each of these to define their music so the texture tells in general terms what the piece is like without completely diving into rhythm, melody, or harmony.
The relative terms to describe texture in the classical senses are density which can be thin (few voices) or think (many voices) or anywhere in between and range which can be narrow or wide or anywhere in between. There is some grey area in these terms though as some people will see things differently like some people may seem two octaves as a wide range and some may call it a narrow range because of different interpretations.
The more concrete classical textures are monophonic, polyphonic, homophonic, and homorhythmic which all describe the melody/harmony relationship.