Someone who is taciturn is reserved, not loud and talkative. The word itself refers to the trait of reticence, of seeming aloof and uncommunicative. A taciturn person might be snobby, naturally quiet, or just shy.
Having its origin in the Latin tacitus, "silent," taciturn came to be used in mid-18th-century English in the sense "habitually silent." Taciturnity is often considered a negative trait, as it suggests someone uncommunicative and too quiet. Jane Austen wrote, "We are each of an unsocial, taciturn disposition, unwilling to speak, unless we expect to say something that will amaze the whole room, and be handed down to posterity with all the éclat of a proverb."