What does 'voice' mean in writing?
The consistent, recognisable quality of a writer's prose — the sum of choices that make one writer's paragraph identifiably theirs. It is frequently discussed mystically and is in fact composed of identifiable elements.
What it is actually made of:
Vocabulary range and register. Whether the writer reaches for plain or elevated words, technical or colloquial, and how consistently.
Sentence rhythm and length. Some writers work in short declaratives; others in long accumulating clauses. This is probably the largest single component, and it is audible.
Syntax habits — where information is placed within a sentence, how frequently subordinate clauses are used, whether the important word arrives early or is held to the end.
Distance and stance. How close the writer stands to the material, and whether they are warm, ironic, clinical or sardonic.
What is noticed. Two writers describing the same room select different details, and selection is character.
Humour, and its absence.
What the writer declines to do — the restraint is as distinctive as the flourish.
Author voice versus character voice. Two different things, frequently confused. Author voice persists across works. Character voice belongs to a narrator or point-of-view character and changes between books — a writer with a strong author voice can still render very different characters, and the ability to do so is a separate skill.
How voice develops. Not by searching for it. The usual account is that it emerges from volume of writing plus wide reading, and that conscious imitation of admired writers is a legitimate stage — most writers pass through obvious influence before the mixture becomes their own.
What suppresses it:
Writing to a perceived expectation rather than to what you actually think.
Over-editing toward neutrality, which is a real risk of heavy line editing — clean prose with no personality.
Fear of being noticed, which produces cautious, hedged writing.
Thesaurus use, which substitutes words the writer does not own.
The reliable test: read it aloud. Voice is largely auditory, and the ear catches falseness the eye misses.