The term 'FLY A PLANE ALONE' can be summarized as 'SOLO' (4 letters). This term refers to the act of flying an aircraft without a co-pilot or other passengers. It is a skill that requires extensive training and experience, as well as a license from the Federal Aviation Administration. Flying SOLO is a challenging but rewarding experience for pilots, as it allows them to take full control of their aircraft and explore the skies on their own.