Found the below link on your website.
but what is considered a "portable" tree stand?
Reason I ask is there has been a metal tree stand on Idaho Dept. of Lands for two years now, and I wonder if it's legal to leave it there year after year. I can send you a picture of it, but it was foggy that morning. Location via maps.google.com and paste in N46 51 48, W115 52 42. Look for the Green arrow.
Idaho Dep't of Lands would be the agency that has jurisdiction and may have an issue with tree stands left on lands they manage.
Idaho Fish and Game only regulates tree stands on property IDFG owns or manages (our Wildlife Management Areas). The Idaho Fish and Game Commission has a rule that prohibits:
construction of blinds, pits, platforms, or tree stands where the soil is disturbed, trees are cut or altered, and artificial fasteners, such as wire, rope, or nails are used. All blinds shall be available to the public on a "first-come - first-served" basis. Portable manufactured blinds and tree stands are allowed but may not be left overnight.
In reference your question asking the definition of Portable the rule is speaking to those commercially built type blinds or tree stands that are easily moved instead of a blind or tree stand you would construct from materials on site.
Again, this rule is specific on to land owned or managed by Idaho Fish and Game and does not apply to lands owned privately, or by any other public agency, such as Idaho Dept. of Lands, US Forest Service, Idaho Parks and Recreation, BLM, etc.