Standbys are people or things that are available to be used when needed. They are usually kept in reserve and are ready to be called upon when necessary. Standbys are often used in the context of emergency services, such as firefighters, police officers, and medical personnel, who are always on call and ready to respond to any situation. In other contexts, standbys can refer to backup equipment or supplies that are kept in case of an emergency. Standbys can also refer to people who are available to fill in for someone else if they are unable to perform their duties.