A Traveling Wave Tube or TWT is rugged thermionic electron tube device for linearly amplifying microwave RF signals. Various models exist according to center frequency, bandwidth, output power, power gain and noise factor. Closely related to Backward Wave Oscillator (BWO) designs in their construction.
It's worth whatever a willing buyer who happens to need one will pay for it. Makes an interesting coffee-table discussion item and would look nice on a curio shelf. Price on eBay is all over the map. Can you guarantee that yours works? Kinda hard to test without a few hundred thousand dollars worth of support equipment. Our resident microwave expert and general all around helpful guy might recognize it and respond to your query. Hope you didn't pay a fortune for that paper weight.