WordPress at a glance
filter is not described

body_class filter-hook . WP 2.8.0

Filters the list of CSS body class names for the current post or page.

Usage

add_filter( 'body_class', 'filter_function_name_5188', 10, 2 );
function filter_function_name_5188( $classes, $class ){
	// filter...

	return $classes;
}
$classes(string[])
An array of body class names.
$class(string[])
An array of additional class names added to the body.

Where the hook is called

get_body_class()
body_class
wp-includes/post-template.php 815
$classes = apply_filters( 'body_class', $classes, $class );

Where the hook is used (in WP core)

Does not used.