Which term refers to an incident involving a sniper?

The term that refers to an incident involving a sniper is "sniper activity." This term specifically addresses situations where a sniper, typically an individual armed with a firearm firing from a concealed position, is involved. Sniper activity can encompass a range of incidents, including but not limited to tactical scenarios, criminal acts, or military engagements.

While the other options refer to specific criminal activities, they do not accurately describe incidents involving snipers. For example, a hostage situation typically involves a person being seized and held against their will, often in a standoff scenario, which might not necessarily include sniper involvement. Armed robbery pertains to stealing with the use of a weapon, and assault with a deadly weapon refers to the act of threatening or inflicting harm using a weapon, neither of which specifically entails the presence of a sniper. Thus, "sniper activity" is the most precise term for an incident involving a sniper.