The kill ring is a global list of blocks of text that were previously copied or moved from buffers.
The kill ring is a list of blocks of text that were previously killed.
Killing moves text from a buffer to the kill ring. Text can also be copied from a buffer to the kill ring, without removing it from the buffer.
There is only one kill ring, shared by all buffers, so you can kill text in one buffer and yank it in another buffer. This is a common way to move text from one buffer to another.
The maximum number of entries in the kill ring is controlled by option
kill-ring-max (which you can customize). If you make a new kill when this limit has been reached, Emacs makes room by deleting the oldest entry in the kill ring.
The actual contents of the kill ring are stored in a variable named
kill-ring; you can view the entire contents of the kill ring using
C-h v kill-ring. See also function
kill-new, which adds a killed or copied string to the kill ring.