vim has 36 named registers: numbers 0-9 and letters a-z
To see what's in all registers:
:reg
Or just specific one(s)
:reg a q
Not only are registers where text is yanked to, but it also stores the contents of vim macros. So you could type qa to start a macro in the a register, press q to finish it, and then view it with :reg q. Or even paste it ("qp), edit it, and then yank it back ("qyy).
There are other registers which I've not yet written down. unnamed, unnamedplus, read only ones, etc.
use the capital letter, eg "Ayy
:reg includes a column for Type.
what does this actually mean?
https://www.brianstorti.com/vim-registers/