Soundstage is how you describe the sound coming from headphones. Specifically, it relates to spatial audio. Headphones will typically give you left and right sound, but when a set of headphones give you a premium soundstage, you'll get noise from all around you - left, right, front, behind, and more. Spatial audio and soundstage are particularly important to gamers, who not only need to hear that someone is creeping up but creeping up from behind on their left.