Historical Rules · 1 February 2012
Rule 701.3d
Official source text from the 1 February 2012 Rules release
To "unattach" an Equipment from a creature means to move it away from that creature so the Equipment is on the battlefield but is not equipping anything. It should no longer be physically touching any creature. If an Aura, Equipment, or Fortification that was attached to something ceases to be attached to it, that counts as "becoming unattached"; this includes if that object and/or that Aura, Equipment, or Fortification leaves the battlefield.