Biosecurity is the set of things people do so that disease does not jump — from farm to farm, from animals to people, from one country to another, or from a lab into the street. On a farm it can look very ordinary: wash your boots, keep visitors out, do not bring leftover meat onto the land, report sick birds at once. At a border it is checks on animals, plants, and food. After bird flu and COVID, news writers use the word more, though actually most people still say “quarantine,” “disease control,” or just “keep it from spreading.” It sits next to biosafety, and people mix them. Biosafety is mostly “do not let the germs in this lab hurt the workers.” Biosecurity is “do not let disease get out into the wider living world.” Governments and farms use it; it is not a kitchen-table word.