Subspace Dimension (colloquially Subspace) is an extension from standard spacetime discovered and used by Synthesis Manufacturing. In short, it's a "pocket dimension" ruled by exotic matter and less defined spacetime which can and is exploited for both energy generation and matter transportation purposes. Current theory suggests that subspace was naturally created with the Big Bang and is a result of matter-antimatter annihilation, in which case both matter and antimatter "slip through" into subspace before turning into exotic matter.
Q: What is subspace?
A: The subspace core itself is a 4 dimensional tunnel / wormhole into subspace, which basically means that the subspace dimension is actually an extension of sorts from standard spacetime. It's basically a pocket dimension ruled by exotic matter and less defined spacetime which can be exploited for both energy and transportation. This explanation is inspired by the theory that the universe was created with both matter and anti-matter, and I wondered what if anti-matter or some other analog to it wasn’t eradicated but simply went somewhere else and became largely unreachable.