what it does:
if defined, changes the visible names, titles, labels in the backend from the default of “WPPizza” to the given value (“my name” in the example below).

affects:
admin/backend only – labels, titles

does not affect:
frontend or any coding references/variables anywhere

usable:
anytime, can also be changed or deleted again at any time.

example:

define('WPPIZZA_NAME', 'my name');/*string*/

where to add/define:

in your wp-config.php before:
/* That's all, stop editing! Happy blogging. */

Disclaimer:
as with all filters, actions and constants:
although these should be safe to use as indicated, there are no guarantees. Use at your own risk. make backups.