The manner in which people express themselves is often referred to as "voice." Voice emanates from the choices that writers make, such as word choice, sentence structure, transitional words, phrasing, beginning and ending strategies, etc. In an author's voice there is a certain tone, or attitude, conveyed. It can convey light-heartedness, gravity, or sarcasm, for instance.
It is often the voice of a writer that attracts or rejects a reader. For instance, in her description of Janie Crawford in Chapter 7 Their Eyes Were Watching God, Zora Neale Hurston writes,
The years took all the fight out of Janie's face....Sometimes she stuck out into the future, imagining her life differently from what it was. But mostly she lived between her hat and her heels, with her emotional disturbances like shade patterns in the woods--come and gone with the sun.
Here in this passage, word choice and figures of speech and natural imagery are expressive of Hurston's voice/style, one that entices the reader's imagination.
Compare this to the bare voice of Ernest Hemingway in this passage from "Cat in the Rain,"
There were only two Americans stopping at the hotel. They did not know any of the people they passed on the stairs on their way to and from their rooms. Their room was on the second floor facing the sea. it also faced the public garden and the war monument.
With its abrupt, separate sentences, Hemingway's voice is that of a mere reporter. The tone that he creates is one of isolation, but it is also factual and leaves little to the imagination. His sparse voice certainly contributes to the isolation of the Americans.
The characteristic way a writer expresses himself is known as the writer's style. Style is made up of many elements, including diction (the words the writer uses) and syntax (the structure of the writer's sentences). While one writer might use sophisticated words and complex sentences, another might use simple words and shorter sentences or some combination.
It can be known as the author's trademark style.