1) n. In New England, it is a brass musical instument, conical in construction, about 18 feet long, with a large mouthpiece, and is the lowest of the brass instruments. It replaced the ophiclede in the symphony orchestra, and has nothing to do with Wagner Tubas. It has only one direct cousin in brass instruments, that being the fluglehorn, for all other brass instruments are more cylindrical than the tuber, even the french horn.
2) n. For the rest of the English-speaking world, it is a fleshy-rooted plant like a potato or a yam. Hence, New Englanders and Non-New Englanders can get confused at times, as evidenced below.

A term used to reference cannabis/marijuana/weed.

A low-class member of the internet comment brigade. Derived from intertube and youtube combined with the fact that many tubers seem to have roughly the intelligence and shape of a potato, this being a different kind of tuber. Tubers can generally be recognized by the fact that their comments bear little to no relevance to the subject at hand.

To smoke from a water pipe. pull a tube.

A Tuber is an Underground root system, you morons. It has to do with plant systems.. Wow.

Someone who enjoys watching adult videos on the internet

taking big fat bong rips... not just the little panzee bongs.... the 3 foot TUBES