WordPress at a glance
filter is not described

minimum_site_name_length filter-hook . WP 4.8.0

Filters the minimum site name length required when validating a site signup.

Usage

add_filter( 'minimum_site_name_length', 'filter_function_name_599' );
function filter_function_name_599( $length ){
	// filter...

	return $length;
}
$length(int)
The minimum site name length.
Default: 4

Where the hook is called

wpmu_validate_blog_signup()
minimum_site_name_length
wp-includes/ms-functions.php 612
$minimum_site_name_length = apply_filters( 'minimum_site_name_length', 4 );

Where the hook is used (in WP core)

Does not used.