Tags are board specific

@Hank Dallmann - You are correct - tags are board specific and not stored in one centralized location. A quick way to copy them from board-to-board is to put them all of the tags on one or more objects, e.g., sticky notes, and copy those objects to another board.

Note that there is a 9 tags per object limit, so if you had 12 tags you are using, you would put 9 tags on one sticky note and the other 3 on a second sticky note and copy those two sticky notes to another board