A sniper was a person who used an accurate long-distance weapon, such as a sniper rifle, on far off targets.
In 2024, while stuck in the Bell Riots, Julian Bashir suggested that the police would put snipers on the roofs across the street from their location and shoot them one at a time. (DS9: "Past Tense, Part II")
MACO Corporal R. Ryan was a sniper. (ENT: "The Xindi", "Anomaly (ENT)", "Chosen Realm")