A "Tube" typically refers to a long, cylindrical object that can be made from various materials like plastic, metal, or glass. It is often used to hold or transport liquids, gases, or other substances. For example, a toothpaste tube is a common household item that allows you to squeeze out just the right amount of paste for brushing your teeth. In a different context, "Tube" can also refer to the London Underground, a rapid transit system in London. It consists of a network of trains that run through tunnels beneath the city, making it easy for people to travel quickly from one place to another.