Noun, slang.
1. A person, most commonly a millennial, who is a gamer, whose great life experiences are almost exclusively indoors, and often defined primarily in terms of virtual explorations, such as those in the
video games Super Smash Bros. and Monster Hunter. A "great indoorsman" could
simultaneously be one of two Smash Bros.
2). A person, most commonly of the nerd varietal, who could go outside, but chooses to spend 99.99% of his or her time inside, often stewing in a pile of his or her own filthy and odorous laundry.
Friend: Are Logan and Jeremy going to the bonfire
tonight?
Other friend: No, those great
indoorsman are going to
hang out in their room to game like fiends until their thumbs bleed.