WordPress at a glance
filter is not described

template filter-hook . WP 1.5.0

Filters the name of the current theme.

Usage

add_filter( 'template', 'filter_function_name_770' );
function filter_function_name_770( $template ){
	// filter...

	return $template;
}
$template(string)
Current theme's directory name.

Where the hook is called

get_template()
template
wp-includes/theme.php 293
return apply_filters( 'template', get_option( 'template' ) );

Where the hook is used (in WP core)

wp-includes/class-wp-customize-manager.php 674
add_filter( 'template', array( $this, 'get_template' ) );
wp-includes/class-wp-customize-manager.php 712
remove_filter( 'template', array( $this, 'get_template' ) );