Flat space

Mostly useful for 3D strategy games, but can be applied to any other instances where movement and positioning in space is limited to two dimensional plane.

For 1st and 3rd person games this could be used to signify that everything of interest is found on the same plane rather than in true 3D space (such as Freelancer, where although you can fly anyway you want, everything of value is placed on a two dimensional plane).

Usually for any game that can be tagged with this also have a direction you can call "up" and "down"... in deep space, even when not spoken in relation to your own or other craft.

Another peculiar trait with this is that the orbit of each planet around a star is on the exact same plane as all the others, including moons and other satellites (which is how they're often depicted in charts, but in reality are far from it).

An "artefact" of this appears in other games (and other media), where all objects in space are aligned so they appear to be "upright", instead of flying whichever happens to be convenient. In real space, objects are far more likely to appear upside down or sideways than entertainment media would have you believe. Most pronounced in cases where spacecraft arrive through warp travel from numerous locations, yet they appear to be perfectly aligned to some strange universal sense of "upright" to sail the invisible sea of space. This is farther taken with disabled or essentially destroyed ships turning over, as if they were leaking seafaring vessels.