Just to expand a little on @ColemenWilson's correct answer, Move/Copy will either move the card completely off one dashboard to another dashboard, or create a LINKED copy on the other dashboard. This can be helpful if you want to update a single card and have those changes reflected on all the cards that have been copied via that method. Doing a SAVE AS creates a totally new and separate card that will have all the same settings as the original card but otherwise not be linked, so changes to either card will not reflect in the other.