Tessaract

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. 


 * A tessaract is in fact a four-dimensional geometric shape, though the term has been adopted by numerous SF works, with differing meanings.