When a project represented by a (sub)tree is finished, you may want to move the tree out of the way and to stop it from contributing to the agenda. Archiving is important to keep your working files compact and global searches like the construction of agenda views fast. The most common archiving action is to move a project tree to another file, the archive file.
C-c C-x C-a
Archive the current entry using the command specified in the variable org-archive-default-command.
C-c C-x C-s or short C-c $
Archive the subtree starting at the cursor position to the location given by org-archive-location.
The default archive location is a file in the same directory as the current file, with the name derived by appending _archive to the current file name. For information and examples on how to change this, see the documentation string of the variable org-archive-location. There is also an in-buffer option for setting this variable, for example
16 July 2011
C-c C-x C-a to archive a branch in emacs org.mode