"Subspace" refers to a smaller space or a subset within a larger space. It is often used in mathematics or physics to describe a space that is contained or related to a larger space. Full definition
Yeah, the environments in Subspace Emissary were pretty generic, yet I really loved it nonetheless, because it was an actual adventure with all the Nintendo characters, and I definitely would want that again, generic environments or not. (gonintendo.com)
While I won't claim the controls and such never bothered me in Subspace Emissary, I simply endured it for the sake of the adventure, and they didn't ruin the overall experience (gonintendo.com)
I found Smash Run to be a fun diversion every now and then, but it won't satisfy players who were hoping for a true side - scrolling adventure mode in the vein of Subspace Emissary from Super Smash Bros.. (tomsguide.com)