trash-directory

trash-directory is a variable defined in `files.el'.
Its value is

nil

Documentation:
Directory for `move-file-to-trash' to move files and directories to.
This directory is only used when the function `system-move-file-to-trash'
is not defined.
Relative paths are interpreted relative to `default-directory'.
If the value is nil, Emacs uses a freedesktop.org-style trashcan.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.2 of Emacs.