Spool can mean one the following:

• Spool, an unflanged plastic cylindrical hub on which magnetic tape is wound in a compact cassette.
• Spool, a usually low-flanged or unflanged cylinder on which thread, wire, cable, paper, or film is wound for distribution and use.
• Bobbin, a cylinder or reel on which a quantity of thread, yarn or wire is wound for use in a particular machine or device.
• Spooling, a physical or metaphorical data storage device in computing.
• Spool, a shaft of a gas turbine engine. Spooling up usually refers to a jet engine spinning up.
• Spool, a large spa/small pool (an insulated inground small pool with spa jets built-in, named by Insulated Water Structures).
• Spool, a verb used to describe a turbocharger or supercharger on a car engine beginning to spin and deliver power.