So, you got yourself a new doodad and are stymied about where to share your joy/disappointment? Never fear, definitions are here!
For the purposes of this forum, an
accessory is anything hard-wired/mounted to the bike itself.
Gear is everything else.
So the Garmin GPS that is hardwired to the bike with an AMPS mount, is an
accessory, a hand-held compass is
gear. Racks and rack-mountable hard/soft bags are
accessories, a duffle bag or backpack that you simply strap to the rack is
gear.
Obviously some items blur the line...don't get too OCD about it, and don't let that make you hesitate sharing your awesome kit!