Master slide outside of a specific presentation
I need a master that is outside a presentation such that multiple presentations can use the same master. Right now I have to create a master and then copy that master to all my presentations. When I need to make a change to the master I have to open every presentation and make the change to each master. If I had one master that every presentation points to I would just have to make the change in one place.
John Korchok commented
This is why PowerPoint includes VBA: so you can write a macro that updates all presentations in a folder.