In Vim, what is the “alternate file”?

Question

I just ran :help registers in Vim and noticed that # \'contains the name of the alternate file\'.

I have seen an example for renaming files

Answer 1

The alternate file is the file that was last edited in the current window. Actually when you use some command to open a new buffer, if the buffer that was displayed had a filename associated with it, that filename is recorded as alternate file name.

See :help alternate-file.