The term 'TUBE TYPE' can refer to four different types of tubes: a triode (6 letters), a DIODE (5 letters), an INNER (5 letters) and a VACUUM (6 letters). A triode is an electronic device consisting of three electrodes, which can be used to amplify signals. A DIODE is a two-terminal electronic component that allows current to flow in one direction only. An INNER tube is a hollow rubber or plastic tube that is inserted into a tire to hold air. Finally, a VACUUM tube is a device that uses a VACUUM to control the flow of electrons.