Source Reference:

• Component: BuddyPress :: bp-members

  File: /bp-members/bp-members-signup.php :: Trac Source Line: 287

  	// Add our slugs to the array and allow them to be filtered
  	$filtered_illegal_names = apply_filters( 'bp_core_illegal_usernames', array_merge( array( 'www', 'web', 'root', 'admin', 'main', 'invite', 'administrator' ), $bp_component_slugs ) );
  
  	// Merge the arrays together
  	$merged_names           = array_merge( (array)$filtered_illegal_names, (array)$db_illegal_names );
  
  	// Remove duplicates
  	$illegal_names          = array_unique( (array)$merged_names );
  
  	return apply_filters( 'bp_core_illegal_names', $illegal_names );
  }
  add_filter( 'pre_update_site_option_illegal_names', 'bp_core_get_illegal_names', 10, 2 );
  
  /**
   * Validate a user name and email address when creating a new user.
   *
   * @global object $wpdb DB Layer
   * @param string $user_name Username to validate
   * @param string $user_email Email address to validate
   * @return array Results of user validation including errors, if any