Sometimes your opponent will play a really powerful Equip Spell Card on a monster and make it too powerful for your monsters to defeat. But there are cards that will let you take that Equip Spell Card and use it for yourself instead.
Cards like "Tailor of the Fickle" can allow you to re-target an Equip Spell Card to a new target. If your opponent played an Equip Spell Card to make his monster stronger, you can switch it to your monster. If you opponent played an Equip Spell Card to make your monster weaker, you can switch it to your opponent's monster and make it weak instead.
The Equip Spell Card does not move and stays on the controller's side of the field. But it re-targets to the new monster of your choice, by the effect of "Tailor of the Fickle", etc.