Texture is how the type appears as a single unit on the page.
This texture is derived from the letterforms, their rhythm, density and how they are arranged: letter to letter, word to word, and line to line on the page. Texture can be compared to fabric - the type is equal to the threads that form it. This captures the essence of the text as a whole, the way the lines of type look as a mass. The way they are arranged in a certain amount of space and their typefaces form the texture.
By altering type's visual darkness, you alter the space it occupies. With variations in light, dark, dense, and volumous, the texture is keyed to the brain's function to identify visual stimuli and the viewer's experience is used to tell the where the eye should travel next.