A tessaract was a theoretical object which, within a three-dimensional exterior, consisted of a limitless interdimensional space.
Captain Montgomery Scott theorized that the ancient device discovered by Rod Portlyn in 2377, which he called "the Zapper", was a tessaract. (CoE eBook: The Art of the Comeback)
- A tessaract is in fact a four-dimensional geometric shape, though the term has been adopted by numerous SF works, with differing meanings.